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Characterization of transparent superconductivity Fe-doped CuCrO2 delafossite oxide
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Characterization of transparent superconductivity Fe-doped CuCrO2 delafossite oxide Chutirat Taddee a , Teerasak Kamwanna b,c,d,∗ , Vittaya Amornkitbamrung b,c,d a
Materials Science and Nanotechnology Program, Faculty of Science, Khon Kaen University, Khon Kaen 40002, Thailand Department of Physics, Faculty of Science, Khon Kaen University, Khon Kaen 40002, Thailand Nanotec-KKU Center of Excellence on Advanced Nanomaterials for Energy Production and Storage, Khon Kaen 40002, Thailand d Integrated Nanotechnology Research Center (INRC), Khon Kaen University, Khon Kaen 40002, Thailand b c
a r t i c l e
i n f o
Article history: Received 15 October 2015 Received in revised form 14 January 2016 Accepted 14 January 2016 Available online xxx Keywords: Transparent conducting oxides Delafossite CuCrO2 Magnetic properties Superconductivity
a b s t r a c t Delafossite CuCr1−x Fex O2 (0.0 ≤ x ≤ 0.15) semiconductors were synthesized using a self-combustion urea nitrate process. The effects of Fe concentration on its microstructural, optical, magnetic, and electrical properties were investigated. X-ray diffraction (XRD) analysis results revealed the delafossite structure in all the samples. The lattice spacing of CuCr1−x Fex O2 slightly increased with increasing substitution of Fe at the Cr sites. The optical properties measured at room temperature using UV–visible spectroscopy showed a weak absorbability in the visible light and near IR regions. The corresponding direct optical band gap was about 3.61 eV, exhibiting transparency in the visible region. The magnetic hysteresis loop measurements showed that the Fe-doped CuCrO2 samples exhibited ferromagnetic behavior at room temperature. This indicated that the substitution of Fe3+ for Cr3+ produced a mixed effect on the magnetic properties of CuCrO2 delafossite oxide. The temperature dependent resistivity measurements clearly revealed the presence of superconductivity in the CuCr1−x Fex O2 with a superconducting transition up to 118 K. © 2016 Elsevier B.V. All rights reserved.
1. Introduction In the past decade, materials with a delafossite-type structure have attracted interest due to their optoelectric, electric and thermoelectric properties [1–6]. Delafossites are p-type wide-bandgap oxide semiconductors. Among them, Cu-based materials are widely studied for transparent conducting oxide (TCOs) applications due to their unique combination of electrical conductivity and optical transparency [2]. Examples of p-type transparent conducting oxides are CuFe1−x Snx O2 [7], CuNdO2 [8], CuFe1−x Crx O2 [9], and CuGaO2 [10]. CuCrO2 has been given considerable attention as a p-type Cu-based delafossite oxide for optoelectronic device applications [11,12], since they contain no precious elements. CuCrO2 reportedly has a bandgap of 3.1 eV and the highest p-type conductivity [13]. The magnetic properties of delafossite oxide have gained attention due to their great potential for applications in diluted magnetic semiconductors (DMSs) [10,14,15], especially applica-
∗ Corresponding author at: Department of Physics, Faculty of Science, Khon Kaen University, Khon Kaen 40002, Thailand. Tel.: +66 846109597. E-mail addresses: [email protected], k [email protected] (T. Kamwanna).
tions for spintronic devices and transparent electronic devices. However, there have been few studies of DMS materials. CuCrO2 shows a paramagnetic to antiferromagnetic transition at ∼23 K. Moreover, CuCrO2 is reported to exhibit ferromagnetic properties [16]. Recently, low-temperature ferromagnetism was realized in Cu(Cr1−x Mx )O2 (M = Mn [17,18], Ni [19,20], Al [21], Rh [22], and Co [14]) ceramics. Furthermore, Cu(Cr1−x Mnx )O2 thin films that exhibited room-temperature ferromagnetism were successfully fabricated [23]. The magnetic structure and the mechanisms responsible for their ferromagnetic properties are still under investigation. Recently, Nakanishi and Katayama-Yoshida suggested a new application of the delafossite structure of CuAlO2 for transparent superconductivity [24]. They calculated the superconducting critical temperature (Tc ) of hole-doped delafossite CuAlO2 based on first-principles calculations. They found that the Tc goes up to about 50 K due to a strong electron–phonon interaction and high phonon frequency caused by the two dimensional flat band at the top of the valence band. This suggests that delafossite oxide may be a promising material for fabricating new superconducting materials. Moreover, no systematic studies of the superconductivity of CuCrO2 have been reported in the literature. Therefore, we systematically investigated the effects of Fe content on superconductivity
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Please cite this article in press as: C. Taddee, et al., Characterization of transparent superconductivity Fe-doped CuCrO2 delafossite oxide, Appl. Surf. Sci. (2016), http://dx.doi.org/10.1016/j.apsusc.2016.01.120
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in CuCrO2 . In this work, CuCr1−x Fex O2 was synthesized using a selfcombustion urea nitrate process. The influences of Fe content on the microstructural, optical, magnetic, and electrical properties of CuCr1−x Fex O2 were systematically investigated. 2. Experiments 2.1. Sample preparations In this work, polycrystalline CuCr1−x Fex O2 (x = 0.01, 0.03, 0.05, 0.10 and 0.15) powders were synthesized using a self-combustion urea nitrate process (UNP). Copper nitrate [Cu(NO3 )2 ·3H2 O, Kanto, purity 99.9%], chromium nitrate [Cr(NO3 )3 ·9H2 O, Kanto, purity 99.9%], iron nitrate [Fe(NO3 )3 9H2 O, Kanto, purity 99.9%], and urea were used as precursor materials. The self-combustion process has been described in detail [25,26]. Briefly, the desired amounts of precursor materials were dissolved in deionize water to form a mixed solution. Urea to nitrate molar ratios of 0.67:1 (UN0.67) and 1:1 (UN1) were used. After continuous stirring at 363 K for 1 h, the precursor solution was heated to 473 K to evaporate water. A highly viscous transparent moisture-sensitive glassy material was obtained. This material was then heated in a crucible on a hot plate at 573 K. The material spontaneously ignited, resulting in a dark green mass. The resulting powder was calcined at 1053 K for 3 h in a N2 atmosphere. The calcined powders were ground and pressed into pellets of 9.5 mm diameter and ∼1 mm thickness by uniaxial compression under a pressure of 250 MPa and then sintered in air at 1273 K for 3 h.
Fig. 1. XRD patterns of calcined CuCrO2 and CuCr1−x Fex O2 powders with Fe contents of x = 0.01, 0.03, 0.05, 0.10 and 0.15.
2.2. Characterization The phase and crystal structure of the synthesized CuCr1−x Fex O2 powders were characterized using x-ray diffraction (XRD). This was done using a Philips PW3040 diffractometer with Cu K˛ radiation ( = 0.15406 nm). The X-ray data were collected using grazing incidence in a diffraction range of 20–80◦ (2) with step width of 0.02◦ . Scanning electron microscope (SEM) images were recorded using a SNE-4500 M SEM, South Korea. Absorption spectroscopy of the calcined powders was obtained for the dry-pressed with the sample holder using a UV-VIS-NIR scanning spectrophotometer (UV-3101PC, Shimadzu) over the range of 200–800 nm at room temperature. Magnetization vs. magnetic field (M–H) curves was developed using a Quantum Design VersaLab 3 Tesla Cryogen-free equipped with a vibrating sample magnetometer (VSM) at room temperature. Temperature dependence of electrical resistivity was measured at temperatures as low as 50 K using the conventional van der Pauw configuration on a Quantum Design VersaLab 3 Tesla Cryogen-free equipment. 3. Results and discussion 3.1. Structural characterization X-ray diffraction measurements were first used to characterize the structure of CuCr1−x Fex O2 . Fig. 1 shows the XRD patterns for calcined powders at room temperature with nominal compositions, where x = 0.01, 0.03, 0.05, 0.10 and 0.15. The standard JCPDS card (No. 89-0539) of CuCrO2 is also shown for comparison. When comparing the measured diffraction peaks of the CuCr1−x Fex O2 with standards, excellent agreement was observed, thus demonstrating that all CuCr1−x Fex O2 samples formed a pure polycrystalline ¯ space group. phase having the delafossite structure within the R3m A secondary phase of CuO was also observed. Furthermore, the relative strength of XRD peaks was different from the standard. It was observed that the polycrystalline grains in the samples with low Fe
Fig. 2. Lattice parameters of calcined CuCr1−x Fex O2 (x = 0.00, 0.01, 0.03, 0.05, 0.10, and 0.15) powders as a function of Fe content.
content, x ≤ 0.05, exhibited a strong preferential alignment along the hexagonal (0 1 2) axis. When the Fe content, x, was ≈0.15, the polycrystalline grains were more aligned on the (0 0 6) axis. This suggested that CuCr1−x Fex O2 grew preferentially along the c-axis. The value of lattice parameters of the delafossite phase of CuCr1−x Fex O2 were calculated using Cohen’s least mean square method and are illustrated in Fig. 2 as a function of Fe content. It was found that the lattice parameters of the calcined powders slightly depended on their Fe content. The extracted lattice parameters a and c increased slightly with Fe substitution. They varied ˚ c = 17.100 A). ˚ slightly from the standard file of JCPDS (a = 2.973 A, Moreover, the lattice parameter, c, increased more rapidly than for ˚ c = 17.093 A˚ for x = 0.00 to a = 2.983 A, ˚ the a-axis (from a = 2.973 A, c = 17.112 A˚ for x = 0.15). This behavior suggested that the ionic radius for a six-fold coordination of Cr3+ was partial substituted 3+ rFe+3 = 0.645 Å ; rCr3+ = 0.615 Å [27]. by the slightly larger Fe The results indicated that the larger ionic radius of Fe3+ increased the number of O–Cu–O dumbbells found parallel to the c-axis. It
Please cite this article in press as: C. Taddee, et al., Characterization of transparent superconductivity Fe-doped CuCrO2 delafossite oxide, Appl. Surf. Sci. (2016), http://dx.doi.org/10.1016/j.apsusc.2016.01.120
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Fig. 3. SEM image of calcined CuCrO2 powder.
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Fig. 5. Extracted direct optical band gaps of calcined CuCr1−x Fex O2 (x = 0.00, 0.01, 0.03, 0.05, 0.10, and 0.15) powders.
increased with increasing Fe content. A strong absorption peak was observed at 285 nm (4.35 eV). This absorption peak was primarily attributed to the charge-transfer excitation from the valence band to the conduction band [28]. The corresponding direct optical band gap (Eg ) was deduced from the relationship between the absorption coefficient and the photon energy (h). It can be expressed as (˛h)2 = A(h − Eg ) [29], where A is a constant. The optical band gap was obtained from a plot of (␣h)2 versus h with a straight-line extrapolation to zero absorption, as shown in Fig. 5. The extracted direct optical band gap of CuCr1−x Fex O2 powders were between 3.53 and 3.63 eV. Reported band gap values were in the range of 3.61-3.99 eV for pure CuCrO2 [30] and 3.15–3.17 eV for thin films [18,31]. The value of the energy gap was larger than 3.1 eV. This indicated that CuCr1−x Fex O2 delafossite can be transparent to photons with energies in the visible light region. 3.3. Magnetic properties
Fig. 4. Absorption spectra of calcined CuCr1−x Fex O2 (x = 0.00, 0.01, 0.03, 0.05, 0.10, and 0.15) powders at room temperature.
was confirmed that the CuCr1−x Fex O2 had (0 0 6) alignment when the Fe content increased. Fig. 3 shows SEM images of calcined CuCrO2 powders. The study revealed that the CuCrO2 powders consisted of irregularly sized hexagonal-like structures with lengths between 2 and 5 m and a thickness of about 1 m. 3.2. Optical properties Optical radiation in the wavelength range between 400 nm and 800 nm is visible light. Optical radiation with wavelengths shorter than 400 nm is ultraviolet (UV) radiation while the wavelengths in the range above 800 nm are infrared (IR) radiation. Fig. 4 shows the optical absorption spectra of calcined CuCr1−x Fex O2 powders obtained in the region between 200 and 800 nm at room temperature. The results clearly showed that all samples had a high absorption coefficient (˛) in the UV light region (250–300 nm) and a weak absorption in the visible light and near IR regions (400–800 nm). It was also observed that absorption above 400 nm
The magnetic properties of calcined CuCr1−x Fex O2 powders were determined using a VSM at room temperature with an applied magnetic field H (−4 kOe ≤ H ≤ 4 kOe), as shown in Fig. 6(a). A linear magnetization dependence on the applied magnetic field revealed clear paramagnetic behavior for the CuCrO2 and CuCr1−x Fex O2 (x = 0.01 and 0.03) calcined powders. Additionally, CuCr1−x Fex O2 with Fe contents above x = 0.05 exhibited ferromagnetic properties, which is reinforced by the observation of a hysteresis loop, although no magnetization saturation was obtained. This was probably caused by the spin-glasslike essence [14,32]. The coercivity values for Fe contents at x = 0.05 and 0.10 were 48.8 and 72.5 Oe, respectively. Magnetization was greatly increased with increasing Fe content. To explore this magnetism, the ionic radii of Cr3+ and Fe3+ should be considered. CuCrO2 compounds exhibit characteristics of ¯ the delafossite group (space group: R3m). In the delafossite structure, each Cu atom is linearly coordinated with two oxygen atoms, resulting in O-Cu-O dumbbells parallel to the c-axis to form a layered triangular lattice antiferromagnet. Moreover, oxygens in the O-Cu-O units are each coordinated with three Cr atoms parallel to the ab plane. The primary effect of partial trivalent ions for Cr3+ was to introduce a structural modulation in the triangular lattice. This leads to multiferroic phase formation [33]. In the current work, XRD measurements showed significant changes in the lattice parameters with increasing Fe content due to the slightly smaller ionic radii of Cr3+ compared to Fe3+ rFe+3 = 0.645 Å ; rCr3+ = 0.615 Å Fe3+ The interaction of the M cations with each other through M–O–M
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Fig. 7. Temperature dependence of resistivity for sintered CuCr1−x Fex O2 (x = 0.00, 0.05 and 0.10) ceramics.
Fig. 6. M–H curves of calcined CuCr1−x Fex O2 powders measured at 300 K for samples prepared using the molar ratios of urea to nitrate of (a) 0.67:1 (UN0.67) and (b) 1:1 (UN1).
linkages of approximately 180o was expected to be the dominant consideration, and that it would be antiferromagnetic in nature [14]. For low Fe contents, short-range interactions of Cr–O–Cr and Cr–O–Fe should not be affected. Therefore, a paramagnetic regime could be obtained. A further increase in Fe content resulted in weak ferromagnetism, which was probably caused by disorder of Cr and Fe in the octahedral sites. The results of short-range interactions of Cr–O–Cr and Cr–O–Fe could give rise to antiferromagnetism coupled with short-range weak ferromagnetism. We present the measured M–H hysteresis for calcined CuCr1−x Fex O2 powders (x = 0.08 and 0.15) with UN1 to further enhance magnetic behavior, as shown in Fig. 6(b). The M–H hysteresis for CuCr0.9 Fe0.1 O2 (UN0.67) is also shown for comparison. It was observed that the hysteresis curve was typically S-shaped with increasing coercivity, giving rise to 170 Oe and a remnant magnetization of ∼0.29 emu/g, although no magnetization saturation was obtained. This indicated that the mixed effects on the magnetic properties of CuCrO2 delafossite oxide at room temperature were caused by substitution of Fe3+ for Cr3+ by and formation of single phase delafossite oxide powder with urea to nitrate in a molar ratio.
[18], and chemical spray pyrolysis grown Mg-doped CuCrO2 thin films (1.7–3.3 cm) [34], but they are comparable to sol-gel grown Fe-doped CuCrO2 thin films (6.25–227 cm) [35], and Mg-doped CuCrO2 thin films (7.34–54.41 cm) [31]. Furthermore, our investigations showed superconducting behavior when the CuCr1−x Fex O2 , in which the resistivity rapidly decreased with decreasing temperature. The critical temperature (Tc ) for superconductors is the temperature at which their electrical resistivity drops to zero. The onset of a sharp drop in resistivity in the CuCrO2 bulk ceramic occurred at 150 K and a superconducting transition occurred at 118 K, which is its zero-resistivity point, as shown in Fig. 7. This Tc value was much higher than the results reported for CsBi4 Te6 (4.4 K) [36], a Cr-doped FeCrx Se alloy (up to 14.1 K) [37], Cu-doped Mg11 B2 bulks ceramics (36.7 K) [38], and for a density functional theory simulation for CuAlO2 (∼50 K) [39]. The observed high Tc can be attributed to strong electron–phonon interactions and high phonon frequencies caused
3.4. Electrical properties Electrical resistivity () was measured for the sintered CuCr1−x Fex O2 ceramics pellets using the van der Pauw configuration. Fig. 7 illustrates the temperature dependence of resistivity between 50 and 400 K for CuCr1−x Fex O2 (x = 0.00, 0.05 and 0.10) ceramics. In the high temperature region, all the delafossite oxides behaved similarly to semiconductors. Their resistivity decreased with increasing temperature. Resistivity at 300 K was found to be 104, 38 and 24 cm for x = 0.00, 0.05 and 0.10, respectively. These values were much higher than those reported for pulsed laser deposition grown Fe-doped CuCrO2 thin films (0.036–0.561 cm)
Fig. 8. Log of the resistivity as a function of the reciprocal temperature for sintered CuCr1−x Fex O2 (x = 0.00, 0.05 and 0.10) ceramics.
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by the two dimensional flat band at the top of the valence band [39]. Additionally, for sintered CuCr1−x Fex O2 ceramic pellets, there were two sharp drops in resistivity at 138 and 107 K. The superconducting transition occurred at 97 and 89 K for x = 0.05 and 0.10, respectively. The decrease in Tc of Fe-doped CuCrO2 can be indicated by the flat band at the top of the valence band, which was affected by the substitution of Fe cations. To investigate the transport mechanisms for delafossite oxide, its thermal activation energy (Ea ) was determined. Ea is often found in semiconductors, and it can be deduced from a linear fit of the Arrhenius relation. The relationship can be expressed as ∼ exp(Ea /kB T), where kB is Boltzmann’s constant [40]. Fig. 8 shows plots of ln vs reciprocal temperature. It can be seen that the resistivity was well fitted with a straight line in the temperature range of 260–380 K. The Ea values were 0.33, 0.27 and 0.28 eV for x = 0.00, 0.05 and 0.10, respectively. These Ea values are comparable to those reported in the literature [31,34,35]. These Ea values observed in Fe-doped CuCrO2 ceramics are the energy required for conduction of charge carriers (holes) in the valence band inducted from the acceptor state within the band gap.
[8]
[9]
[10]
[11] [12] [13]
[14]
[15]
[16]
[17]
4. Conclusions CuCr1−x Fex O2 powders were successfully synthesized using a self-combustion urea nitrate process. XRD analysis results revealed the formation of a delafossite structure. The optical band energy gap for the direct optical band transition was determined to be 3.53–3.63 eV, exhibiting transparency in the visible region. The magnetic measurements for Fe-doped CuCrO2 samples showed weak ferromagnetism at room temperature, which was reinforced by the observation of a hysteresis loop. This behavior indicates that the substitution of Fe3+ for Cr3+ produced a mixed effect on the magnetic properties of this delafossite oxide. The temperature dependent resistivity measurements clearly revealed the presence of superconductivity in the CuCr1−x Fex O2 with a superconducting transition up to 118 K. Our study demonstrated that transparent superconductivity derived in delafossite oxide can be a viable approach for exploration of novel superconductors.
[18]
[19]
[20]
[21]
[22]
[23]
[24]
[25]
Acknowledgements [26]
This work was financially supported by the Institute for the Promotion of Teaching Science and Technology (IPST under Contract No. 010/2555) and the Nanotechnology Center (NANOTEC), NSTDA, Ministry of Science and Technology, Thailand, through its program of Center of Excellence Network and the Integrated Nanotechnology Research Center (INRC), Khon Kaen University, Thailand.
[27]
[28]
[29]
References [30] [1] H. Kawazoe, M. Yasukawa, H. Hyodo, M. Kurita, H. Yanagi, H. Hosono, P-type electrical conduction in transparent thin films of CuAlO2 , Nature 389 (1997) 939–942. [2] M.A. Marquardt, N.A. Ashmore, D.P. Cann, Crystal chemistry and electrical properties of the delafossite structure, Thin Solid Films 496 (2006) 146–156. [3] S. Sheng, G. Fang, C. Li, S. Xu, X. Zhao, p-type transparent conducting oxides, Phys. Status Solidi 203 (2006) 1891–1900. [4] H. Yanagi, T. Hase, S. Ibuki, K. Ueda, H. Hosono, Bipolarity in electrical conduction of transparent oxide semiconductor CuInO2 with delafossite structure, Appl. Phys. Lett. 78 (2001) 1583. [5] K. El Ataoui, J.-P. Doumerc, A. Ammar, J.-C. Grenier, L. Fournès, A. Wattiaux, et al., Delafossite oxides containing vanadium(III): preparation and magnetic properties, Solid State Sci. 7 (2005) 710–717. [6] K. Isawa, Y. Yaegashi, S. Ogota, M. Nagano, S. Sudo, K. Yamada, et al., Thermoelectric power of delafossite-derived compounds, RCuO2+ı (R = Y, La, Pr, Nd, Sm, and Eu), Phys. Rev. B: Condens. Matter Mater. Phys. 57 (1998) 7950–7954. [7] C. Ruttanapun, B. Boonchom, M. Thongkam, S. Kongtaweelert, C. Thanachayanont, A. Wichainchai, Electrical and optical properties of p-type
[31]
[32]
[33]
[34]
[35] [36]
5
CuFe1−x Snx O2 (x = 0.03 0.05) delafossite-oxide, J. Appl. Phys. 113 (2013) 023103. G. Dong, M. Zhang, M. Wang, F. Tang, H. Li, A. Huang, et al., Synthesis, electrical and optical properties of CuNdO2 compound, J. Phys. Chem. Solids 73 (2012) 1170–1172. M. Lalanne, A. Barnabé, F. Mathieu, P. Tailhades, Synthesis and thermostructural studies of a CuFe1−x Crx O2 delafossite solid solution with 0 ≤ x ≤ 1, Inorg. Chem. 48 (2009) 6065–6071. F. Jlaiel, T. Elkhouni, M. Amami, P. Strobel, A. Ben Salah, Structural and physical properties of the (Ca, Mg)-doped delafossite powder CuGaO2 , Mater. Res. Bull. 48 (2013) 1020–1026. D.O. Scanlon, G.W. Watson, Understanding the p-type defect chemistry of CuCrO2 , J. Mater. Chem. 21 (2011) 3655–3663. R.-S. Yu, C.-P. Tasi, Structure, composition and properties of p-type CuCrO2 thin films, Ceram. Int. 40 (2014) 8211–8217. J. Tate, M.K. Jayaraj, A.D. Draeseke, T. Ulbrich, A.W. Sleight, K.A. Vanaja, et al., p-Type oxides for use in transparent diodes, Thin Solid Films 411 (2002) 119–124. T. Elkhouni, M. Amami, C.V. Colin, P. Strobel, A. Ben Salah, Synthesis, structural and magnetic studies of the CuCr1 −x Cox O2 delafossite oxide, J. Magn. Magn. Mater. 330 (2013) 101–105. C. Gao, F. Lin, X. Zhou, W. Shi, A. Liu, Fe concentration dependences of microstructure and magnetic properties for Cu(Cr1−x Fex )O2 ceramics, J. Alloys Compd. 565 (2013) 154–158. S. Seki, Y. Onose, Y. Tokura, Spin-driven ferroelectricity in triangular lattice antiferromagnets ACrO2 (A = Cu, Ag, Li, or Na), Phys. Rev. Lett. 101 (2008) 67204. D. Li, X. Fang, W. Dong, Z. Deng, R. Tao, S. Zhou, et al., Magnetic and electrical properties of p-type Mn-doped CuCrO2 semiconductors, J. Phys. D: Appl. Phys. 42 (2009) 055009. F. Lin, C. Gao, X. Zhou, W. Shi, A. Liu, Magnetic, electrical and optical properties of p-type Fe-doped CuCrO2 semiconductor thin films, J. Alloys Compd. 581 (2013) 502–507. S. Luo, K.F. Wang, S.Z. Li, X.W. Dong, Z.B. Yan, H.L. Cai, et al., Enhanced ferromagnetism and ferroelectricity in multiferroic CuCr1−x Nix O2 , Appl. Phys. Lett. 94 (2009) 172504. S. Luo, L. Li, K.F. Wang, S.Z. Li, X.W. Dong, Z.B. Yan, et al., Enhanced magnetic and ferroelectric properties of multiferroic CuCrO2 by Ni-doping, Thin Solid Films 518 (2010) e50–e53. M. Amami, C.V. Colin, P. Strobel, A. Ben Salah, Al-doping effect on the structural and physical properties of delafossite-type oxide CuCrO2 , Phys. B: Condens. Matter 406 (2011) 2182–2185. F. Jlaiel, M. Amami, N. Boudjada, P. Strobel, A. Ben Salah, Metal transition doping effect on the structural and physical properties of delafossite-type oxide CuCrO2 , J. Alloys Compd. 509 (2011) 7784–7788. Y.F. Wang, Y.J. Gu, T. Wang, W.Z. Shi, Magnetic, optical and electrical properties of Mn-doped CuCrO2 thin films prepared by chemical solution deposition method, J. Sol-Gel Sci. Technol. 59 (2011) 222–227. A. Nakanishi, H. Katayama-Yoshida, Computational materials design for superconductivity in hole-doped delafossite CuAlO2 : transparent superconductors, Solid State Commun. 152 (2012) 24–27. T.-W. Chiu, P.-S. Huang, Preparation of delafossite CuFeO2 coral-like powder using a self-combustion glycine nitrate process, Ceram. Int. 39 (2013) S575–S578. T.-W. Chiu, B.-S. Yu, Y.-R. Wang, K.-T. Chen, Y.-T. Lin, Synthesis of nanosized CuCrO2 porous powders via a self-combustion glycine nitrate process, J. Alloys Compd. 509 (2011) 2933–2935. R.D. Shannon, Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides, Acta Crystallogr. 32 (1976) 751–767. H. Hiraga, T. Makino, T. Fukumura, H. Weng, M. Kawasaki, Electronic structure of the delafossite-type CuMO2 (M = Sc, Cr, Mn, Fe, and Co): optical absorption measurements and first-principles calculations, Phys. Rev. B 84 (2011) 41411. Y. Li, W. Bo, M. Zhong, Y. Hu, M. Zhu, H. Zhang, et al., The morphology and optical properties of ZnO crystals fabricated by hydrothermal method under pulsed magnetic field, Phys. Stat. Solidi 10 (2013) 1276–1279. M. Asemi, M. Ghanaatshoar, Preparation of CuCrO2 nanoparticles with narrow size distribution by sol–gel method, J. Sol-Gel Sci. Technol. 70 (2014) 416–421. Y. Wang, Y. Gu, T. Wang, W. Shi, Structural, optical and electrical properties of Mg-doped CuCrO2 thin films by sol–gel processing, J. Alloys Compd. 509 (2011) 5897–5902. M.M. Moharam, M.M. Rashad, E.M. Elsayed, R.M. Abou-Shahba, A facile novel synthesis of delafossite CuFeO2 powders, J. Mater. Sci. Mater. Electron. 25 (2014) 1798–1803. L. Naka-in, T. Kamwanna, P. Srepusharawoot, S. Pinitsoontorn, V. Amornkitbamrung, Effects of Ge substitution on the structural and physical properties of CuFeO2 delafossite oxide, Jpn. J. Appl. Phys. 54 (2015) 04DH10. S.H. Lim, S. Desu, A.C. Rastogi, Chemical spray pyrolysis deposition and characterization of p-type CuCr1-x Mgx O2 transparent oxide semiconductor thin films, J. Phys. Chem. Solids 69 (2008) 2047–2056. H.-Y. Chen, K.-P. Chang, C.-C. Yang, Characterization of transparent conductive delafossite-CuCr1−x O2 films, Appl. Surf. Sci. 273 (2013) 324–329. C.D. Malliakas, D.Y. Chung, H. Claus, M.G. Kanatzidis, Superconductivity in the narrow-gap semiconductor CsBi4 Te6 , J. Am. Chem. Soc. 135 (2013) 14540–14543.
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[37] S. Kumar, P.P. Singh, Electronic properties of excess Cr in FeCrx Se alloy, Solid State Commun. 220 (2015) 49–56. [38] F. Cheng, Y. Liu, Z. Ma, H. Li, M. Shahriar Al Hossain, Superior critical current density obtained in Mg11 B2 low activation superconductor by using reactive amorphous 11 B and optimizing sintering temperature, J. Alloys Compd. 650 (2015) 508–513.
[39] A. Nakanishi, H. Katayama-Yoshida, Chemical trend of superconducting transition temperature in hole-doped delafossite of CuAlO2 , AgAlO2 and AuAlO2 , Solid State Commun. 152 (2012) 2078–2081. [40] T. Okuda, N. Jufuku, S. Hidaka, N. Terada, Magnetic, transport, and thermoelectric properties of the delafossite oxides CuCr1−x Mgx O2 (0 ≤ x ≤ 0.04), Phys. Rev. B 72 (2005) 144403.
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Characterization of transparent superconductivity Fe-doped CuCrO2 delafossite oxide Chutirat Taddee a , Teerasak Kamwanna b,c,d,∗ , Vittaya Amornkitbamrung b,c,d a
Materials Science and Nanotechnology Program, Faculty of Science, Khon Kaen University, Khon Kaen 40002, Thailand Department of Physics, Faculty of Science, Khon Kaen University, Khon Kaen 40002, Thailand Nanotec-KKU Center of Excellence on Advanced Nanomaterials for Energy Production and Storage, Khon Kaen 40002, Thailand d Integrated Nanotechnology Research Center (INRC), Khon Kaen University, Khon Kaen 40002, Thailand b c
a r t i c l e
i n f o
Article history: Received 15 October 2015 Received in revised form 14 January 2016 Accepted 14 January 2016 Available online xxx Keywords: Transparent conducting oxides Delafossite CuCrO2 Magnetic properties Superconductivity
a b s t r a c t Delafossite CuCr1−x Fex O2 (0.0 ≤ x ≤ 0.15) semiconductors were synthesized using a self-combustion urea nitrate process. The effects of Fe concentration on its microstructural, optical, magnetic, and electrical properties were investigated. X-ray diffraction (XRD) analysis results revealed the delafossite structure in all the samples. The lattice spacing of CuCr1−x Fex O2 slightly increased with increasing substitution of Fe at the Cr sites. The optical properties measured at room temperature using UV–visible spectroscopy showed a weak absorbability in the visible light and near IR regions. The corresponding direct optical band gap was about 3.61 eV, exhibiting transparency in the visible region. The magnetic hysteresis loop measurements showed that the Fe-doped CuCrO2 samples exhibited ferromagnetic behavior at room temperature. This indicated that the substitution of Fe3+ for Cr3+ produced a mixed effect on the magnetic properties of CuCrO2 delafossite oxide. The temperature dependent resistivity measurements clearly revealed the presence of superconductivity in the CuCr1−x Fex O2 with a superconducting transition up to 118 K. © 2016 Elsevier B.V. All rights reserved.
1. Introduction In the past decade, materials with a delafossite-type structure have attracted interest due to their optoelectric, electric and thermoelectric properties [1–6]. Delafossites are p-type wide-bandgap oxide semiconductors. Among them, Cu-based materials are widely studied for transparent conducting oxide (TCOs) applications due to their unique combination of electrical conductivity and optical transparency [2]. Examples of p-type transparent conducting oxides are CuFe1−x Snx O2 [7], CuNdO2 [8], CuFe1−x Crx O2 [9], and CuGaO2 [10]. CuCrO2 has been given considerable attention as a p-type Cu-based delafossite oxide for optoelectronic device applications [11,12], since they contain no precious elements. CuCrO2 reportedly has a bandgap of 3.1 eV and the highest p-type conductivity [13]. The magnetic properties of delafossite oxide have gained attention due to their great potential for applications in diluted magnetic semiconductors (DMSs) [10,14,15], especially applica-
∗ Corresponding author at: Department of Physics, Faculty of Science, Khon Kaen University, Khon Kaen 40002, Thailand. Tel.: +66 846109597. E-mail addresses: [email protected], k [email protected] (T. Kamwanna).
tions for spintronic devices and transparent electronic devices. However, there have been few studies of DMS materials. CuCrO2 shows a paramagnetic to antiferromagnetic transition at ∼23 K. Moreover, CuCrO2 is reported to exhibit ferromagnetic properties [16]. Recently, low-temperature ferromagnetism was realized in Cu(Cr1−x Mx )O2 (M = Mn [17,18], Ni [19,20], Al [21], Rh [22], and Co [14]) ceramics. Furthermore, Cu(Cr1−x Mnx )O2 thin films that exhibited room-temperature ferromagnetism were successfully fabricated [23]. The magnetic structure and the mechanisms responsible for their ferromagnetic properties are still under investigation. Recently, Nakanishi and Katayama-Yoshida suggested a new application of the delafossite structure of CuAlO2 for transparent superconductivity [24]. They calculated the superconducting critical temperature (Tc ) of hole-doped delafossite CuAlO2 based on first-principles calculations. They found that the Tc goes up to about 50 K due to a strong electron–phonon interaction and high phonon frequency caused by the two dimensional flat band at the top of the valence band. This suggests that delafossite oxide may be a promising material for fabricating new superconducting materials. Moreover, no systematic studies of the superconductivity of CuCrO2 have been reported in the literature. Therefore, we systematically investigated the effects of Fe content on superconductivity
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in CuCrO2 . In this work, CuCr1−x Fex O2 was synthesized using a selfcombustion urea nitrate process. The influences of Fe content on the microstructural, optical, magnetic, and electrical properties of CuCr1−x Fex O2 were systematically investigated. 2. Experiments 2.1. Sample preparations In this work, polycrystalline CuCr1−x Fex O2 (x = 0.01, 0.03, 0.05, 0.10 and 0.15) powders were synthesized using a self-combustion urea nitrate process (UNP). Copper nitrate [Cu(NO3 )2 ·3H2 O, Kanto, purity 99.9%], chromium nitrate [Cr(NO3 )3 ·9H2 O, Kanto, purity 99.9%], iron nitrate [Fe(NO3 )3 9H2 O, Kanto, purity 99.9%], and urea were used as precursor materials. The self-combustion process has been described in detail [25,26]. Briefly, the desired amounts of precursor materials were dissolved in deionize water to form a mixed solution. Urea to nitrate molar ratios of 0.67:1 (UN0.67) and 1:1 (UN1) were used. After continuous stirring at 363 K for 1 h, the precursor solution was heated to 473 K to evaporate water. A highly viscous transparent moisture-sensitive glassy material was obtained. This material was then heated in a crucible on a hot plate at 573 K. The material spontaneously ignited, resulting in a dark green mass. The resulting powder was calcined at 1053 K for 3 h in a N2 atmosphere. The calcined powders were ground and pressed into pellets of 9.5 mm diameter and ∼1 mm thickness by uniaxial compression under a pressure of 250 MPa and then sintered in air at 1273 K for 3 h.
Fig. 1. XRD patterns of calcined CuCrO2 and CuCr1−x Fex O2 powders with Fe contents of x = 0.01, 0.03, 0.05, 0.10 and 0.15.
2.2. Characterization The phase and crystal structure of the synthesized CuCr1−x Fex O2 powders were characterized using x-ray diffraction (XRD). This was done using a Philips PW3040 diffractometer with Cu K˛ radiation ( = 0.15406 nm). The X-ray data were collected using grazing incidence in a diffraction range of 20–80◦ (2) with step width of 0.02◦ . Scanning electron microscope (SEM) images were recorded using a SNE-4500 M SEM, South Korea. Absorption spectroscopy of the calcined powders was obtained for the dry-pressed with the sample holder using a UV-VIS-NIR scanning spectrophotometer (UV-3101PC, Shimadzu) over the range of 200–800 nm at room temperature. Magnetization vs. magnetic field (M–H) curves was developed using a Quantum Design VersaLab 3 Tesla Cryogen-free equipped with a vibrating sample magnetometer (VSM) at room temperature. Temperature dependence of electrical resistivity was measured at temperatures as low as 50 K using the conventional van der Pauw configuration on a Quantum Design VersaLab 3 Tesla Cryogen-free equipment. 3. Results and discussion 3.1. Structural characterization X-ray diffraction measurements were first used to characterize the structure of CuCr1−x Fex O2 . Fig. 1 shows the XRD patterns for calcined powders at room temperature with nominal compositions, where x = 0.01, 0.03, 0.05, 0.10 and 0.15. The standard JCPDS card (No. 89-0539) of CuCrO2 is also shown for comparison. When comparing the measured diffraction peaks of the CuCr1−x Fex O2 with standards, excellent agreement was observed, thus demonstrating that all CuCr1−x Fex O2 samples formed a pure polycrystalline ¯ space group. phase having the delafossite structure within the R3m A secondary phase of CuO was also observed. Furthermore, the relative strength of XRD peaks was different from the standard. It was observed that the polycrystalline grains in the samples with low Fe
Fig. 2. Lattice parameters of calcined CuCr1−x Fex O2 (x = 0.00, 0.01, 0.03, 0.05, 0.10, and 0.15) powders as a function of Fe content.
content, x ≤ 0.05, exhibited a strong preferential alignment along the hexagonal (0 1 2) axis. When the Fe content, x, was ≈0.15, the polycrystalline grains were more aligned on the (0 0 6) axis. This suggested that CuCr1−x Fex O2 grew preferentially along the c-axis. The value of lattice parameters of the delafossite phase of CuCr1−x Fex O2 were calculated using Cohen’s least mean square method and are illustrated in Fig. 2 as a function of Fe content. It was found that the lattice parameters of the calcined powders slightly depended on their Fe content. The extracted lattice parameters a and c increased slightly with Fe substitution. They varied ˚ c = 17.100 A). ˚ slightly from the standard file of JCPDS (a = 2.973 A, Moreover, the lattice parameter, c, increased more rapidly than for ˚ c = 17.093 A˚ for x = 0.00 to a = 2.983 A, ˚ the a-axis (from a = 2.973 A, c = 17.112 A˚ for x = 0.15). This behavior suggested that the ionic radius for a six-fold coordination of Cr3+ was partial substituted 3+ rFe+3 = 0.645 Å ; rCr3+ = 0.615 Å [27]. by the slightly larger Fe The results indicated that the larger ionic radius of Fe3+ increased the number of O–Cu–O dumbbells found parallel to the c-axis. It
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Fig. 3. SEM image of calcined CuCrO2 powder.
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Fig. 5. Extracted direct optical band gaps of calcined CuCr1−x Fex O2 (x = 0.00, 0.01, 0.03, 0.05, 0.10, and 0.15) powders.
increased with increasing Fe content. A strong absorption peak was observed at 285 nm (4.35 eV). This absorption peak was primarily attributed to the charge-transfer excitation from the valence band to the conduction band [28]. The corresponding direct optical band gap (Eg ) was deduced from the relationship between the absorption coefficient and the photon energy (h). It can be expressed as (˛h)2 = A(h − Eg ) [29], where A is a constant. The optical band gap was obtained from a plot of (␣h)2 versus h with a straight-line extrapolation to zero absorption, as shown in Fig. 5. The extracted direct optical band gap of CuCr1−x Fex O2 powders were between 3.53 and 3.63 eV. Reported band gap values were in the range of 3.61-3.99 eV for pure CuCrO2 [30] and 3.15–3.17 eV for thin films [18,31]. The value of the energy gap was larger than 3.1 eV. This indicated that CuCr1−x Fex O2 delafossite can be transparent to photons with energies in the visible light region. 3.3. Magnetic properties
Fig. 4. Absorption spectra of calcined CuCr1−x Fex O2 (x = 0.00, 0.01, 0.03, 0.05, 0.10, and 0.15) powders at room temperature.
was confirmed that the CuCr1−x Fex O2 had (0 0 6) alignment when the Fe content increased. Fig. 3 shows SEM images of calcined CuCrO2 powders. The study revealed that the CuCrO2 powders consisted of irregularly sized hexagonal-like structures with lengths between 2 and 5 m and a thickness of about 1 m. 3.2. Optical properties Optical radiation in the wavelength range between 400 nm and 800 nm is visible light. Optical radiation with wavelengths shorter than 400 nm is ultraviolet (UV) radiation while the wavelengths in the range above 800 nm are infrared (IR) radiation. Fig. 4 shows the optical absorption spectra of calcined CuCr1−x Fex O2 powders obtained in the region between 200 and 800 nm at room temperature. The results clearly showed that all samples had a high absorption coefficient (˛) in the UV light region (250–300 nm) and a weak absorption in the visible light and near IR regions (400–800 nm). It was also observed that absorption above 400 nm
The magnetic properties of calcined CuCr1−x Fex O2 powders were determined using a VSM at room temperature with an applied magnetic field H (−4 kOe ≤ H ≤ 4 kOe), as shown in Fig. 6(a). A linear magnetization dependence on the applied magnetic field revealed clear paramagnetic behavior for the CuCrO2 and CuCr1−x Fex O2 (x = 0.01 and 0.03) calcined powders. Additionally, CuCr1−x Fex O2 with Fe contents above x = 0.05 exhibited ferromagnetic properties, which is reinforced by the observation of a hysteresis loop, although no magnetization saturation was obtained. This was probably caused by the spin-glasslike essence [14,32]. The coercivity values for Fe contents at x = 0.05 and 0.10 were 48.8 and 72.5 Oe, respectively. Magnetization was greatly increased with increasing Fe content. To explore this magnetism, the ionic radii of Cr3+ and Fe3+ should be considered. CuCrO2 compounds exhibit characteristics of ¯ the delafossite group (space group: R3m). In the delafossite structure, each Cu atom is linearly coordinated with two oxygen atoms, resulting in O-Cu-O dumbbells parallel to the c-axis to form a layered triangular lattice antiferromagnet. Moreover, oxygens in the O-Cu-O units are each coordinated with three Cr atoms parallel to the ab plane. The primary effect of partial trivalent ions for Cr3+ was to introduce a structural modulation in the triangular lattice. This leads to multiferroic phase formation [33]. In the current work, XRD measurements showed significant changes in the lattice parameters with increasing Fe content due to the slightly smaller ionic radii of Cr3+ compared to Fe3+ rFe+3 = 0.645 Å ; rCr3+ = 0.615 Å Fe3+ The interaction of the M cations with each other through M–O–M
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Fig. 7. Temperature dependence of resistivity for sintered CuCr1−x Fex O2 (x = 0.00, 0.05 and 0.10) ceramics.
Fig. 6. M–H curves of calcined CuCr1−x Fex O2 powders measured at 300 K for samples prepared using the molar ratios of urea to nitrate of (a) 0.67:1 (UN0.67) and (b) 1:1 (UN1).
linkages of approximately 180o was expected to be the dominant consideration, and that it would be antiferromagnetic in nature [14]. For low Fe contents, short-range interactions of Cr–O–Cr and Cr–O–Fe should not be affected. Therefore, a paramagnetic regime could be obtained. A further increase in Fe content resulted in weak ferromagnetism, which was probably caused by disorder of Cr and Fe in the octahedral sites. The results of short-range interactions of Cr–O–Cr and Cr–O–Fe could give rise to antiferromagnetism coupled with short-range weak ferromagnetism. We present the measured M–H hysteresis for calcined CuCr1−x Fex O2 powders (x = 0.08 and 0.15) with UN1 to further enhance magnetic behavior, as shown in Fig. 6(b). The M–H hysteresis for CuCr0.9 Fe0.1 O2 (UN0.67) is also shown for comparison. It was observed that the hysteresis curve was typically S-shaped with increasing coercivity, giving rise to 170 Oe and a remnant magnetization of ∼0.29 emu/g, although no magnetization saturation was obtained. This indicated that the mixed effects on the magnetic properties of CuCrO2 delafossite oxide at room temperature were caused by substitution of Fe3+ for Cr3+ by and formation of single phase delafossite oxide powder with urea to nitrate in a molar ratio.
[18], and chemical spray pyrolysis grown Mg-doped CuCrO2 thin films (1.7–3.3 cm) [34], but they are comparable to sol-gel grown Fe-doped CuCrO2 thin films (6.25–227 cm) [35], and Mg-doped CuCrO2 thin films (7.34–54.41 cm) [31]. Furthermore, our investigations showed superconducting behavior when the CuCr1−x Fex O2 , in which the resistivity rapidly decreased with decreasing temperature. The critical temperature (Tc ) for superconductors is the temperature at which their electrical resistivity drops to zero. The onset of a sharp drop in resistivity in the CuCrO2 bulk ceramic occurred at 150 K and a superconducting transition occurred at 118 K, which is its zero-resistivity point, as shown in Fig. 7. This Tc value was much higher than the results reported for CsBi4 Te6 (4.4 K) [36], a Cr-doped FeCrx Se alloy (up to 14.1 K) [37], Cu-doped Mg11 B2 bulks ceramics (36.7 K) [38], and for a density functional theory simulation for CuAlO2 (∼50 K) [39]. The observed high Tc can be attributed to strong electron–phonon interactions and high phonon frequencies caused
3.4. Electrical properties Electrical resistivity () was measured for the sintered CuCr1−x Fex O2 ceramics pellets using the van der Pauw configuration. Fig. 7 illustrates the temperature dependence of resistivity between 50 and 400 K for CuCr1−x Fex O2 (x = 0.00, 0.05 and 0.10) ceramics. In the high temperature region, all the delafossite oxides behaved similarly to semiconductors. Their resistivity decreased with increasing temperature. Resistivity at 300 K was found to be 104, 38 and 24 cm for x = 0.00, 0.05 and 0.10, respectively. These values were much higher than those reported for pulsed laser deposition grown Fe-doped CuCrO2 thin films (0.036–0.561 cm)
Fig. 8. Log of the resistivity as a function of the reciprocal temperature for sintered CuCr1−x Fex O2 (x = 0.00, 0.05 and 0.10) ceramics.
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by the two dimensional flat band at the top of the valence band [39]. Additionally, for sintered CuCr1−x Fex O2 ceramic pellets, there were two sharp drops in resistivity at 138 and 107 K. The superconducting transition occurred at 97 and 89 K for x = 0.05 and 0.10, respectively. The decrease in Tc of Fe-doped CuCrO2 can be indicated by the flat band at the top of the valence band, which was affected by the substitution of Fe cations. To investigate the transport mechanisms for delafossite oxide, its thermal activation energy (Ea ) was determined. Ea is often found in semiconductors, and it can be deduced from a linear fit of the Arrhenius relation. The relationship can be expressed as ∼ exp(Ea /kB T), where kB is Boltzmann’s constant [40]. Fig. 8 shows plots of ln vs reciprocal temperature. It can be seen that the resistivity was well fitted with a straight line in the temperature range of 260–380 K. The Ea values were 0.33, 0.27 and 0.28 eV for x = 0.00, 0.05 and 0.10, respectively. These Ea values are comparable to those reported in the literature [31,34,35]. These Ea values observed in Fe-doped CuCrO2 ceramics are the energy required for conduction of charge carriers (holes) in the valence band inducted from the acceptor state within the band gap.
[8]
[9]
[10]
[11] [12] [13]
[14]
[15]
[16]
[17]
4. Conclusions CuCr1−x Fex O2 powders were successfully synthesized using a self-combustion urea nitrate process. XRD analysis results revealed the formation of a delafossite structure. The optical band energy gap for the direct optical band transition was determined to be 3.53–3.63 eV, exhibiting transparency in the visible region. The magnetic measurements for Fe-doped CuCrO2 samples showed weak ferromagnetism at room temperature, which was reinforced by the observation of a hysteresis loop. This behavior indicates that the substitution of Fe3+ for Cr3+ produced a mixed effect on the magnetic properties of this delafossite oxide. The temperature dependent resistivity measurements clearly revealed the presence of superconductivity in the CuCr1−x Fex O2 with a superconducting transition up to 118 K. Our study demonstrated that transparent superconductivity derived in delafossite oxide can be a viable approach for exploration of novel superconductors.
[18]
[19]
[20]
[21]
[22]
[23]
[24]
[25]
Acknowledgements [26]
This work was financially supported by the Institute for the Promotion of Teaching Science and Technology (IPST under Contract No. 010/2555) and the Nanotechnology Center (NANOTEC), NSTDA, Ministry of Science and Technology, Thailand, through its program of Center of Excellence Network and the Integrated Nanotechnology Research Center (INRC), Khon Kaen University, Thailand.
[27]
[28]
[29]
References [30] [1] H. Kawazoe, M. Yasukawa, H. Hyodo, M. Kurita, H. Yanagi, H. Hosono, P-type electrical conduction in transparent thin films of CuAlO2 , Nature 389 (1997) 939–942. [2] M.A. Marquardt, N.A. Ashmore, D.P. Cann, Crystal chemistry and electrical properties of the delafossite structure, Thin Solid Films 496 (2006) 146–156. [3] S. Sheng, G. Fang, C. Li, S. Xu, X. Zhao, p-type transparent conducting oxides, Phys. Status Solidi 203 (2006) 1891–1900. [4] H. Yanagi, T. Hase, S. Ibuki, K. Ueda, H. Hosono, Bipolarity in electrical conduction of transparent oxide semiconductor CuInO2 with delafossite structure, Appl. Phys. Lett. 78 (2001) 1583. [5] K. El Ataoui, J.-P. Doumerc, A. Ammar, J.-C. Grenier, L. Fournès, A. Wattiaux, et al., Delafossite oxides containing vanadium(III): preparation and magnetic properties, Solid State Sci. 7 (2005) 710–717. [6] K. Isawa, Y. Yaegashi, S. Ogota, M. Nagano, S. Sudo, K. Yamada, et al., Thermoelectric power of delafossite-derived compounds, RCuO2+ı (R = Y, La, Pr, Nd, Sm, and Eu), Phys. Rev. B: Condens. Matter Mater. Phys. 57 (1998) 7950–7954. [7] C. Ruttanapun, B. Boonchom, M. Thongkam, S. Kongtaweelert, C. Thanachayanont, A. Wichainchai, Electrical and optical properties of p-type
[31]
[32]
[33]
[34]
[35] [36]
5
CuFe1−x Snx O2 (x = 0.03 0.05) delafossite-oxide, J. Appl. Phys. 113 (2013) 023103. G. Dong, M. Zhang, M. Wang, F. Tang, H. Li, A. Huang, et al., Synthesis, electrical and optical properties of CuNdO2 compound, J. Phys. Chem. Solids 73 (2012) 1170–1172. M. Lalanne, A. Barnabé, F. Mathieu, P. Tailhades, Synthesis and thermostructural studies of a CuFe1−x Crx O2 delafossite solid solution with 0 ≤ x ≤ 1, Inorg. Chem. 48 (2009) 6065–6071. F. Jlaiel, T. Elkhouni, M. Amami, P. Strobel, A. Ben Salah, Structural and physical properties of the (Ca, Mg)-doped delafossite powder CuGaO2 , Mater. Res. Bull. 48 (2013) 1020–1026. D.O. Scanlon, G.W. Watson, Understanding the p-type defect chemistry of CuCrO2 , J. Mater. Chem. 21 (2011) 3655–3663. R.-S. Yu, C.-P. Tasi, Structure, composition and properties of p-type CuCrO2 thin films, Ceram. Int. 40 (2014) 8211–8217. J. Tate, M.K. Jayaraj, A.D. Draeseke, T. Ulbrich, A.W. Sleight, K.A. Vanaja, et al., p-Type oxides for use in transparent diodes, Thin Solid Films 411 (2002) 119–124. T. Elkhouni, M. Amami, C.V. Colin, P. Strobel, A. Ben Salah, Synthesis, structural and magnetic studies of the CuCr1 −x Cox O2 delafossite oxide, J. Magn. Magn. Mater. 330 (2013) 101–105. C. Gao, F. Lin, X. Zhou, W. Shi, A. Liu, Fe concentration dependences of microstructure and magnetic properties for Cu(Cr1−x Fex )O2 ceramics, J. Alloys Compd. 565 (2013) 154–158. S. Seki, Y. Onose, Y. Tokura, Spin-driven ferroelectricity in triangular lattice antiferromagnets ACrO2 (A = Cu, Ag, Li, or Na), Phys. Rev. Lett. 101 (2008) 67204. D. Li, X. Fang, W. Dong, Z. Deng, R. Tao, S. Zhou, et al., Magnetic and electrical properties of p-type Mn-doped CuCrO2 semiconductors, J. Phys. D: Appl. Phys. 42 (2009) 055009. F. Lin, C. Gao, X. Zhou, W. Shi, A. Liu, Magnetic, electrical and optical properties of p-type Fe-doped CuCrO2 semiconductor thin films, J. Alloys Compd. 581 (2013) 502–507. S. Luo, K.F. Wang, S.Z. Li, X.W. Dong, Z.B. Yan, H.L. Cai, et al., Enhanced ferromagnetism and ferroelectricity in multiferroic CuCr1−x Nix O2 , Appl. Phys. Lett. 94 (2009) 172504. S. Luo, L. Li, K.F. Wang, S.Z. Li, X.W. Dong, Z.B. Yan, et al., Enhanced magnetic and ferroelectric properties of multiferroic CuCrO2 by Ni-doping, Thin Solid Films 518 (2010) e50–e53. M. Amami, C.V. Colin, P. Strobel, A. Ben Salah, Al-doping effect on the structural and physical properties of delafossite-type oxide CuCrO2 , Phys. B: Condens. Matter 406 (2011) 2182–2185. F. Jlaiel, M. Amami, N. Boudjada, P. Strobel, A. Ben Salah, Metal transition doping effect on the structural and physical properties of delafossite-type oxide CuCrO2 , J. Alloys Compd. 509 (2011) 7784–7788. Y.F. Wang, Y.J. Gu, T. Wang, W.Z. Shi, Magnetic, optical and electrical properties of Mn-doped CuCrO2 thin films prepared by chemical solution deposition method, J. Sol-Gel Sci. Technol. 59 (2011) 222–227. A. Nakanishi, H. Katayama-Yoshida, Computational materials design for superconductivity in hole-doped delafossite CuAlO2 : transparent superconductors, Solid State Commun. 152 (2012) 24–27. T.-W. Chiu, P.-S. Huang, Preparation of delafossite CuFeO2 coral-like powder using a self-combustion glycine nitrate process, Ceram. Int. 39 (2013) S575–S578. T.-W. Chiu, B.-S. Yu, Y.-R. Wang, K.-T. Chen, Y.-T. Lin, Synthesis of nanosized CuCrO2 porous powders via a self-combustion glycine nitrate process, J. Alloys Compd. 509 (2011) 2933–2935. R.D. Shannon, Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides, Acta Crystallogr. 32 (1976) 751–767. H. Hiraga, T. Makino, T. Fukumura, H. Weng, M. Kawasaki, Electronic structure of the delafossite-type CuMO2 (M = Sc, Cr, Mn, Fe, and Co): optical absorption measurements and first-principles calculations, Phys. Rev. B 84 (2011) 41411. Y. Li, W. Bo, M. Zhong, Y. Hu, M. Zhu, H. Zhang, et al., The morphology and optical properties of ZnO crystals fabricated by hydrothermal method under pulsed magnetic field, Phys. Stat. Solidi 10 (2013) 1276–1279. M. Asemi, M. Ghanaatshoar, Preparation of CuCrO2 nanoparticles with narrow size distribution by sol–gel method, J. Sol-Gel Sci. Technol. 70 (2014) 416–421. Y. Wang, Y. Gu, T. Wang, W. Shi, Structural, optical and electrical properties of Mg-doped CuCrO2 thin films by sol–gel processing, J. Alloys Compd. 509 (2011) 5897–5902. M.M. Moharam, M.M. Rashad, E.M. Elsayed, R.M. Abou-Shahba, A facile novel synthesis of delafossite CuFeO2 powders, J. Mater. Sci. Mater. Electron. 25 (2014) 1798–1803. L. Naka-in, T. Kamwanna, P. Srepusharawoot, S. Pinitsoontorn, V. Amornkitbamrung, Effects of Ge substitution on the structural and physical properties of CuFeO2 delafossite oxide, Jpn. J. Appl. Phys. 54 (2015) 04DH10. S.H. Lim, S. Desu, A.C. Rastogi, Chemical spray pyrolysis deposition and characterization of p-type CuCr1-x Mgx O2 transparent oxide semiconductor thin films, J. Phys. Chem. Solids 69 (2008) 2047–2056. H.-Y. Chen, K.-P. Chang, C.-C. Yang, Characterization of transparent conductive delafossite-CuCr1−x O2 films, Appl. Surf. Sci. 273 (2013) 324–329. C.D. Malliakas, D.Y. Chung, H. Claus, M.G. Kanatzidis, Superconductivity in the narrow-gap semiconductor CsBi4 Te6 , J. Am. Chem. Soc. 135 (2013) 14540–14543.
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[37] S. Kumar, P.P. Singh, Electronic properties of excess Cr in FeCrx Se alloy, Solid State Commun. 220 (2015) 49–56. [38] F. Cheng, Y. Liu, Z. Ma, H. Li, M. Shahriar Al Hossain, Superior critical current density obtained in Mg11 B2 low activation superconductor by using reactive amorphous 11 B and optimizing sintering temperature, J. Alloys Compd. 650 (2015) 508–513.
[39] A. Nakanishi, H. Katayama-Yoshida, Chemical trend of superconducting transition temperature in hole-doped delafossite of CuAlO2 , AgAlO2 and AuAlO2 , Solid State Commun. 152 (2012) 2078–2081. [40] T. Okuda, N. Jufuku, S. Hidaka, N. Terada, Magnetic, transport, and thermoelectric properties of the delafossite oxides CuCr1−x Mgx O2 (0 ≤ x ≤ 0.04), Phys. Rev. B 72 (2005) 144403.
Please cite this article in press as: C. Taddee, et al., Characterization of transparent superconductivity Fe-doped CuCrO2 delafossite oxide, Appl. Surf. Sci. (2016), http://dx.doi.org/10.1016/j.apsusc.2016.01.120