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Dielectric characteristics of Ga doped TbMnO3
Materials Science and Engineering B 178 (2013) 316–320
Contents lists available at SciVerse ScienceDirect
Materials Science and Engineering B journal homepage: www.elsevier.com/locate/mseb
Short communication
Dielectric characteristics of Ga doped TbMnO3 Jianxun Xu, Yimin Cui ∗ Key Laboratory of Micro-nano Measurement-Manipulation and Physics (Ministry of Education), Department of Physics, Beihang University, Beijing 100191, China
a r t i c l e
i n f o
Article history: Received 24 June 2012 Received in revised form 7 November 2012 Accepted 25 November 2012 Available online 28 December 2012 Keywords: Manganites Ga doped TbMnO3 Dielectric characteristics
a b s t r a c t Low-frequency (0.1–200 kHz) dielectric properties of Tb1−x Gax MnO3 and TbGay Mn1−y O3 (x, y = 0.05, 0.1, 0.2, 0.3, 0.4) ceramic composites, which were synthesized by conventional solid-state reaction, were investigated in the temperature range from 77 to 350 K. Both dielectric constants and loss tangent (tan ı) increase with increasing temperature and decrease with increasing frequency, respectively. Interestingly, the dielectric constants of Tb1−x Gax MnO3 are as large as that of the parent TbMnO3 , while the loss tangent reduces remarkably and less than 1 at high frequencies. These improvements demonstrate that Ga doped TbMnO3 may have potential applications. © 2012 Elsevier B.V. All rights reserved.
1. Introduction
2. Experiment
In recent years, there are more and more studies on transitionmetal oxide materials for their potential applications [1–3]. TbMnO3 (TMO), a typical transition-metal perovskite oxide, shows exotic properties such as ferroelectric, antiferromagnetism and their coupling effects [4–6], which may be used in information storage, sensors and other new novel devices. Recently, there are some reports about cation doped TMO and their valuable electric–magnetic properties [7–11]. Yang et al. [7] have proved that oxygen content can affect the magnetic structures of both Mn and Tb in Na-doped TMO. Cui [8] has reported that TMO by adding different doses of TiO2 show obvious difference in dielectric constants and dielectric loss. Pérez et al. [9] demonstrated that magnetic properties of TMO were influenced by doping with Al. Blasco et al. [10,11] found that magnetic properties exhibit different changes as the Ca content increases. However, most of the above researches focus on the properties of Tb1−x Ax MnO3 (A is metal cation) at low temperature [5,7,11–15]. In our recent work, we found remarkable physical properties changes in TMO films induced by Ga ion implantation (to be published elsewhere) [16]. For comparison, Tb1−x Gax MnO3 and TbGay Mn1−y O3 (x, y = 0.05, 0.1, 0.2, 0.3, 0.4) were fabricated by conventional solid-state reaction method. The low-frequency dielectric properties were examined from 77 to 350 K.
Tb1−x Gax MnO3 (x = 0.05, 0.1, 0.2, 0.3, 0.4) and TbGay Mn1−y O3 (y = 0.05, 0.1, 0.2, 0.3, 0.4) samples were prepared by conventional solid-state reaction. The stoichiometric amounts of Tb4 O7 , MnO2 and Ga2 O3 powders with high purity (not less than 99.99%), were mixed and grounded in an agate mortar and sintered at 1200–1300 ◦ C in air for 12 h repeatedly. Next the disk samples about 6 mm in diameter and 2 mm in thickness were pressed, and sintered at 1400 ◦ C in air for another 12 h and then cooled down to room temperature with furnace. All of the ten samples were characterized by X-ray diffraction (XRD) at room temperature using Cu K␣ radiations as the X-ray source. Surface morphology of bulks was measured by scanning electron microscopy (SEM, Model: S4800). Temperature dependent dielectric properties (capacitances and dielectric loss) were measured using a QuadTech ZM2353 LCR Digibridge in a frequency range of 40–200 kHz. Electrodes were made by coating silver paste on both sides of the disk-type samples.
∗ Corresponding author. Tel.: +86 10 82339567; fax: +86 10 82339567. E-mail addresses: [email protected], [email protected] (Y. Cui). 0921-5107/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.mseb.2012.11.025
3. Results and discussion The XRD patterns of the ten samples are shown in Fig. 1. The crystalline phases of the low content doped composites show almost same patterns compared with the parent TbMnO3 , which indicates those samples are single phase. However, high proportion Ga doped composites, such as x = 0.2, 0.3, 0.4, y = 0.3, 0.4, show more or less miscellaneous peaks, especially at 36◦ (2), which are the patterns of additional phases of Ga2 O3 in Tb1−x Gax MnO3 (x = 0.2, 0.3, 0.4) and TbGay Mn1−y O3 (y = 0.4) and more obvious with the Ga content increasing. From the intensities of the peaks, it can
J. Xu, Y. Cui / Materials Science and Engineering B 178 (2013) 316–320
317
Fig. 1. The XRD patterns for (a) TMO, Tb1−x Gax MnO3 (red sign, the same blow) and (b) TMO, TbGay Mn1−y O3 (blue sign, the same blow) composites. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)
be concluded that the doping with high Ga content are difficult in TbMnO3 . The typical scanning electron micrographs are illustrated in Fig. 2. The ceramic samples are porous and have different size of grains. Although these samples were prepared using the same pressure and sintering time, it is clearly observed that the grains of Tb1−x Gax MnO3 are larger than that of TbGay Mn1−y O3 , which may be caused by the additional phases of Ga2 O3 .
Fig. 3(a) shows the dependence of dielectric constants with temperature for the ten samples at 100 kHz. Dielectric constants are given by the following equation: ε =
Cd Sε0
(1)
where C is the capacitance between the two plates, d is the thickness of the sample, S is the area of the round face painted silver
Fig. 2. The typical scanning electron micrographs of the polycrystalline Tb1−x Gax MnO3 and TbGay Mn1−y O3 samples.
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Fig. 3. The temperature dependence of (a) the dielectric constant ε and (b) the dielectric loss tan ı of ten composites at 100 kHz.
paste, and ε0 is the permittivity of vacuum. All the dielectric constants increase with increasing temperature. Obviously, when the temperature is higher than 160 K, the dielectric constants of Tb1−x Gax MnO3 are larger than that of TbGay Mn1−y O3 . Fig. 3(b) shows the dependence of dielectric loss with temperature for the ten samples at 100 kHz. All the dielectric loss also increase with increasing temperature, which show remarkable increasing (switching) at low temperature and turn flat at high temperature. It is clear that the switching temperature of Tb1−x Gax MnO3 is lower than that of TbGay Mn1−y O3 in the curves. The dielectric constants of the five samples of Tb1−x Gax MnO3 are obviously higher than that of the other five of TbGay Mn1−y O3 . At the same time, all the doped
samples have lower dielectric loss compared with that of the parent TbMnO3 . Fig. 4(a) and (c) shows the dependence of dielectric constants with temperature in a range from 77 to 350 K for Tb0.95 Ga0.05 MnO3 and TbGa0.05 Mn0.95 O3 samples, respectively. In Fig. 4(a), the Tb0.95 Ga0.05 MnO3 sample shows about 1000-fold increase in ε with increasing temperature followed by the occurrence of a broad peak at a characteristic temperature which are strongly affected by the frequency. With the increasing frequency, the dielectric constants decrease obviously at the same temperature. Two dielectric plateaus can be observed at low and high temperatures respectively, between which the dielectric constants boost steeply, accompanied by a peak in the loss tangent. The relaxation process makes the electric dipoles freeze at low temperature and there exists a decay in polarization with respect to the applied electric field, which is the evidence of the steeply drop in ε [17]. At high temperature, the localized holes result conductivity through the hopping, which makes dipolar effect and considerable polarization, so the large values of ε can be observed when the temperature exceeds 250 K [8]. In Fig. 4(a) and (c), the increase in dielectric constants is more pronounced at lower frequencies than that at high frequencies. Specially, the samples of TbGay Mn1−y O3 show almost the same dielectric constants in the low temperature and high frequency ranges. Fig. 4(b) and (d) shows the temperature dependent of the dielectric loss (tan ı). The dielectric loss increase with increasing temperature and indicate obvious one or two wide dielectric dissipation peaks, which appear at the characteristic temperatures corresponding to the sharp changes in ε . The temperatures of the dissipation peaks shift to high temperature range as the frequency increasing, which shows the thermally excited relaxation process, and it is attributed to the direct current (DC) conductivity. With increasing temperature and decreasing frequency, the influence of the DC conductivity is more significant. Intriguingly, the dielectric loss of Tb0.95 Ga0.05 MnO3 is almost less than 1 in high frequency range, which is quite different with high dielectric loss of TbMnO3 at room temperature [17]. Fig. 5(a) and (c) shows the dependence of dielectric constants with frequency for the ten samples at 220 K and 350 K separately. The figures depict that all the samples exhibit dielectric dispersion. The dielectric constants of the ten samples are high and
Fig. 4. The temperature dependence of (a) the dielectric constant ε and (b) the loss tangent tan ı of Tb0.95 Ga0.05 MnO3 , (c) the dielectric constant ε and (d) the loss tangent tan ı of TbGa0.05 Mn0.95 O3 , the frequency range is 0.1–200 kHz.
J. Xu, Y. Cui / Materials Science and Engineering B 178 (2013) 316–320
319
Fig. 5. The frequency dependence of (a) the dielectric constant ε and (b) the dielectric loss tan ı of ten composites at 220 K, (c) the dielectric constant ε and (d) the dielectric loss tan ı at 350 K.
Fig. 6. The frequency dependence of (a) the dielectric constant ε and (b) the imaginary dielectric constant ε of Tb0.9 Ga0.1 MnO3 , (c) the dielectric constant ε and (d) the imaginary dielectric constant ε of TbGa0.1 Mn0.9 O3 at fixed temperatures from 77 to 350 K.
decrease with increasing frequency. Remarkably, the constants of Tb1−x Gax MnO3 are universally higher than that of TbGay Mn1−y O3 . Especially, the dielectric constants of Tb0.8 Ga0.2 MnO3 are the highest at all measurement frequencies. Fig. 5(b) and (d) shows the dependence of dielectric loss with frequency at 220 K and 350 K separately. For the ten samples, the dielectric loss decrease with increasing frequency and increase rapidly at low frequencies. For Tb0.9 Ga0.1 MnO3 and TbGa0.1 Mn0.9 O3 samples, the frequency dependence of real (ε ) and imaginary (ε ) parts, where ε = ε · tan ı, of the complex permittivity are showed in Fig. 6. As shown in Fig. 6(a) and (c), most of the curves drop non-linearly with the increasing temperature. And below 100 K the nearly horizontal lines in the figures suggest the dielectric constants do not change with frequencies. The frequency dependence of ε shown in Fig. 6(b) and (d) present that most experimental data fall on a straight line in the frequency range covered, which indicates
that the conductivity has main contribution to ε [18]. With the decreasing temperature, the data points of ε deviate from the straight line at T < 210 K. This phenomenon is the condensation of the polarized clusters. Owing to the condensation of small clusters, the size of microdomains increase, in which the slow dynamics of the domain walls contribute to the delay of the response to the external alternating field, particularly at high frequencies [19]. 4. Conclusion In summary, by doping Ga ion into TMO, the prominent changes are observed in dielectric constants and loss tangent of the ten TMO samples. Two dielectric plateaus appear at lower and higher temperatures respectively, between which the dielectric constants boost steeply, and accompanied by a peak in the loss tangent. It is quite different with the parent TMO that the dielectric loss
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of Tb1−x Gax MnO3 is low in a wide temperature range even at room temperature. XRD patterns indicate that the doping with high Ga content are difficult in TbMnO3 . And compared with TbGay Mn1−y O3 , Tb1−x Gax MnO3 samples have larger grains, which may contributed to the larger dielectric constants and higher switching temperatures. The curves of ε with frequency fall on a straight line at T > 210 K, which indicating that the conductivity has main contribution to the electrical processes. Acknowledgement We acknowledge the financial support from National Natural Science Foundation of China (No. 10975013). References [1] S. Jin, T.H. Tiefel, M. McCormack, R.A. Fastnacht, R. Ramesh, L.H. Chen, Science 264 (1993) 413. [2] A. Asamitsu, Y. Moritomo, Y. Tomioka, T. Arima, Y. Tokura, Nature (London) 373 (1995) 407. [3] A. Tiwari, K.P. Rajeev, J. Narayan, Solid State Communications 121 (2002) 357. [4] T. Kimura, T. Goto, H. Shintani, K. Ishizaka, T. Arima, Y. Tokura, Nature 426 (2003) 55.
[5] T. Goto, T. Kimura, G. Lawes, A.P. Ramirez, Y. Tokura, Physical Review Letters 92 (2004) 257201. [6] Y.M. Cui, Y.F. Tian, W. Liu, Y.F. Li, R.M. Wang, T. Wu, AIP Advances 1 (2011) 042129. [7] C.C. Yang, M.K. Chung, W.H. Li, T.S. Chan, R.S. Liu, Y.H. Lien, C.Y. Huang, Y.Y. Chan, Y.D. Yao, J.W. Lynn, Physical Review B 74 (2006) 094409. [8] Y.M. Cui, Physica B 403 (2008) 2963. [9] F. Pérez, J. Heiras, R. Escudero, Physica Status Solidi (c) 4 (2007) 4049. [10] J. Blasco, C. Ritter, J. García, J.M. de Teresa, J. Pérez-Cacho, M.R. Ibarra, Physical Review B 62 (2000) 5609. [11] N. Mufti, A.A. Nugroho, G.R. Blake, T.T.M. Palstra, Physical Review B 78 (2008) 024109. [12] T. Kimura, G. Lawes, T. Goto, Y. Tokura, A.P. Ramirez, Physical Review B 71 (2005) 224425. [13] J.A. Alonso, M.J. Martinez-Lope, M.T. Casais, M.T. Fernandez-Diaz, Inorganic Chemistry 39 (2000) 917. [14] T. Goto, Y. Yamasaki, H. Watanable, T. Kimura, Y. Tokura, Physical Review B 72 (2005) 220703. [15] A. Pimenov, A.A. Mukhin, V. Yu Ivanov, V.D. Travkin, A.M. Balbashov, A. Loidl, Nature Physics 2 (2006) 97. [16] H. Luo, R. Jing, Y.M. Cui, H.L. Wang, R.M. Wang, Progress in Natural Science: Materials International 20 (2010) 111. [17] J.B. Wu, C.W. Nan, Y.H. Lin, Y. Deng, Physical Review Letters 89 (2004) 217601. [18] Y.M. Cui, L.W. Liu, G.L. Xie, R.M. Wang, Solid State Communications 138 (2006) 481. [19] C.C. Wang, Y.M. Cui, G.L. Xie, C.P. Chen, L.W. Zhang, Physical Review B 72 (2005) 064513.
Contents lists available at SciVerse ScienceDirect
Materials Science and Engineering B journal homepage: www.elsevier.com/locate/mseb
Short communication
Dielectric characteristics of Ga doped TbMnO3 Jianxun Xu, Yimin Cui ∗ Key Laboratory of Micro-nano Measurement-Manipulation and Physics (Ministry of Education), Department of Physics, Beihang University, Beijing 100191, China
a r t i c l e
i n f o
Article history: Received 24 June 2012 Received in revised form 7 November 2012 Accepted 25 November 2012 Available online 28 December 2012 Keywords: Manganites Ga doped TbMnO3 Dielectric characteristics
a b s t r a c t Low-frequency (0.1–200 kHz) dielectric properties of Tb1−x Gax MnO3 and TbGay Mn1−y O3 (x, y = 0.05, 0.1, 0.2, 0.3, 0.4) ceramic composites, which were synthesized by conventional solid-state reaction, were investigated in the temperature range from 77 to 350 K. Both dielectric constants and loss tangent (tan ı) increase with increasing temperature and decrease with increasing frequency, respectively. Interestingly, the dielectric constants of Tb1−x Gax MnO3 are as large as that of the parent TbMnO3 , while the loss tangent reduces remarkably and less than 1 at high frequencies. These improvements demonstrate that Ga doped TbMnO3 may have potential applications. © 2012 Elsevier B.V. All rights reserved.
1. Introduction
2. Experiment
In recent years, there are more and more studies on transitionmetal oxide materials for their potential applications [1–3]. TbMnO3 (TMO), a typical transition-metal perovskite oxide, shows exotic properties such as ferroelectric, antiferromagnetism and their coupling effects [4–6], which may be used in information storage, sensors and other new novel devices. Recently, there are some reports about cation doped TMO and their valuable electric–magnetic properties [7–11]. Yang et al. [7] have proved that oxygen content can affect the magnetic structures of both Mn and Tb in Na-doped TMO. Cui [8] has reported that TMO by adding different doses of TiO2 show obvious difference in dielectric constants and dielectric loss. Pérez et al. [9] demonstrated that magnetic properties of TMO were influenced by doping with Al. Blasco et al. [10,11] found that magnetic properties exhibit different changes as the Ca content increases. However, most of the above researches focus on the properties of Tb1−x Ax MnO3 (A is metal cation) at low temperature [5,7,11–15]. In our recent work, we found remarkable physical properties changes in TMO films induced by Ga ion implantation (to be published elsewhere) [16]. For comparison, Tb1−x Gax MnO3 and TbGay Mn1−y O3 (x, y = 0.05, 0.1, 0.2, 0.3, 0.4) were fabricated by conventional solid-state reaction method. The low-frequency dielectric properties were examined from 77 to 350 K.
Tb1−x Gax MnO3 (x = 0.05, 0.1, 0.2, 0.3, 0.4) and TbGay Mn1−y O3 (y = 0.05, 0.1, 0.2, 0.3, 0.4) samples were prepared by conventional solid-state reaction. The stoichiometric amounts of Tb4 O7 , MnO2 and Ga2 O3 powders with high purity (not less than 99.99%), were mixed and grounded in an agate mortar and sintered at 1200–1300 ◦ C in air for 12 h repeatedly. Next the disk samples about 6 mm in diameter and 2 mm in thickness were pressed, and sintered at 1400 ◦ C in air for another 12 h and then cooled down to room temperature with furnace. All of the ten samples were characterized by X-ray diffraction (XRD) at room temperature using Cu K␣ radiations as the X-ray source. Surface morphology of bulks was measured by scanning electron microscopy (SEM, Model: S4800). Temperature dependent dielectric properties (capacitances and dielectric loss) were measured using a QuadTech ZM2353 LCR Digibridge in a frequency range of 40–200 kHz. Electrodes were made by coating silver paste on both sides of the disk-type samples.
∗ Corresponding author. Tel.: +86 10 82339567; fax: +86 10 82339567. E-mail addresses: [email protected], [email protected] (Y. Cui). 0921-5107/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.mseb.2012.11.025
3. Results and discussion The XRD patterns of the ten samples are shown in Fig. 1. The crystalline phases of the low content doped composites show almost same patterns compared with the parent TbMnO3 , which indicates those samples are single phase. However, high proportion Ga doped composites, such as x = 0.2, 0.3, 0.4, y = 0.3, 0.4, show more or less miscellaneous peaks, especially at 36◦ (2), which are the patterns of additional phases of Ga2 O3 in Tb1−x Gax MnO3 (x = 0.2, 0.3, 0.4) and TbGay Mn1−y O3 (y = 0.4) and more obvious with the Ga content increasing. From the intensities of the peaks, it can
J. Xu, Y. Cui / Materials Science and Engineering B 178 (2013) 316–320
317
Fig. 1. The XRD patterns for (a) TMO, Tb1−x Gax MnO3 (red sign, the same blow) and (b) TMO, TbGay Mn1−y O3 (blue sign, the same blow) composites. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)
be concluded that the doping with high Ga content are difficult in TbMnO3 . The typical scanning electron micrographs are illustrated in Fig. 2. The ceramic samples are porous and have different size of grains. Although these samples were prepared using the same pressure and sintering time, it is clearly observed that the grains of Tb1−x Gax MnO3 are larger than that of TbGay Mn1−y O3 , which may be caused by the additional phases of Ga2 O3 .
Fig. 3(a) shows the dependence of dielectric constants with temperature for the ten samples at 100 kHz. Dielectric constants are given by the following equation: ε =
Cd Sε0
(1)
where C is the capacitance between the two plates, d is the thickness of the sample, S is the area of the round face painted silver
Fig. 2. The typical scanning electron micrographs of the polycrystalline Tb1−x Gax MnO3 and TbGay Mn1−y O3 samples.
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Fig. 3. The temperature dependence of (a) the dielectric constant ε and (b) the dielectric loss tan ı of ten composites at 100 kHz.
paste, and ε0 is the permittivity of vacuum. All the dielectric constants increase with increasing temperature. Obviously, when the temperature is higher than 160 K, the dielectric constants of Tb1−x Gax MnO3 are larger than that of TbGay Mn1−y O3 . Fig. 3(b) shows the dependence of dielectric loss with temperature for the ten samples at 100 kHz. All the dielectric loss also increase with increasing temperature, which show remarkable increasing (switching) at low temperature and turn flat at high temperature. It is clear that the switching temperature of Tb1−x Gax MnO3 is lower than that of TbGay Mn1−y O3 in the curves. The dielectric constants of the five samples of Tb1−x Gax MnO3 are obviously higher than that of the other five of TbGay Mn1−y O3 . At the same time, all the doped
samples have lower dielectric loss compared with that of the parent TbMnO3 . Fig. 4(a) and (c) shows the dependence of dielectric constants with temperature in a range from 77 to 350 K for Tb0.95 Ga0.05 MnO3 and TbGa0.05 Mn0.95 O3 samples, respectively. In Fig. 4(a), the Tb0.95 Ga0.05 MnO3 sample shows about 1000-fold increase in ε with increasing temperature followed by the occurrence of a broad peak at a characteristic temperature which are strongly affected by the frequency. With the increasing frequency, the dielectric constants decrease obviously at the same temperature. Two dielectric plateaus can be observed at low and high temperatures respectively, between which the dielectric constants boost steeply, accompanied by a peak in the loss tangent. The relaxation process makes the electric dipoles freeze at low temperature and there exists a decay in polarization with respect to the applied electric field, which is the evidence of the steeply drop in ε [17]. At high temperature, the localized holes result conductivity through the hopping, which makes dipolar effect and considerable polarization, so the large values of ε can be observed when the temperature exceeds 250 K [8]. In Fig. 4(a) and (c), the increase in dielectric constants is more pronounced at lower frequencies than that at high frequencies. Specially, the samples of TbGay Mn1−y O3 show almost the same dielectric constants in the low temperature and high frequency ranges. Fig. 4(b) and (d) shows the temperature dependent of the dielectric loss (tan ı). The dielectric loss increase with increasing temperature and indicate obvious one or two wide dielectric dissipation peaks, which appear at the characteristic temperatures corresponding to the sharp changes in ε . The temperatures of the dissipation peaks shift to high temperature range as the frequency increasing, which shows the thermally excited relaxation process, and it is attributed to the direct current (DC) conductivity. With increasing temperature and decreasing frequency, the influence of the DC conductivity is more significant. Intriguingly, the dielectric loss of Tb0.95 Ga0.05 MnO3 is almost less than 1 in high frequency range, which is quite different with high dielectric loss of TbMnO3 at room temperature [17]. Fig. 5(a) and (c) shows the dependence of dielectric constants with frequency for the ten samples at 220 K and 350 K separately. The figures depict that all the samples exhibit dielectric dispersion. The dielectric constants of the ten samples are high and
Fig. 4. The temperature dependence of (a) the dielectric constant ε and (b) the loss tangent tan ı of Tb0.95 Ga0.05 MnO3 , (c) the dielectric constant ε and (d) the loss tangent tan ı of TbGa0.05 Mn0.95 O3 , the frequency range is 0.1–200 kHz.
J. Xu, Y. Cui / Materials Science and Engineering B 178 (2013) 316–320
319
Fig. 5. The frequency dependence of (a) the dielectric constant ε and (b) the dielectric loss tan ı of ten composites at 220 K, (c) the dielectric constant ε and (d) the dielectric loss tan ı at 350 K.
Fig. 6. The frequency dependence of (a) the dielectric constant ε and (b) the imaginary dielectric constant ε of Tb0.9 Ga0.1 MnO3 , (c) the dielectric constant ε and (d) the imaginary dielectric constant ε of TbGa0.1 Mn0.9 O3 at fixed temperatures from 77 to 350 K.
decrease with increasing frequency. Remarkably, the constants of Tb1−x Gax MnO3 are universally higher than that of TbGay Mn1−y O3 . Especially, the dielectric constants of Tb0.8 Ga0.2 MnO3 are the highest at all measurement frequencies. Fig. 5(b) and (d) shows the dependence of dielectric loss with frequency at 220 K and 350 K separately. For the ten samples, the dielectric loss decrease with increasing frequency and increase rapidly at low frequencies. For Tb0.9 Ga0.1 MnO3 and TbGa0.1 Mn0.9 O3 samples, the frequency dependence of real (ε ) and imaginary (ε ) parts, where ε = ε · tan ı, of the complex permittivity are showed in Fig. 6. As shown in Fig. 6(a) and (c), most of the curves drop non-linearly with the increasing temperature. And below 100 K the nearly horizontal lines in the figures suggest the dielectric constants do not change with frequencies. The frequency dependence of ε shown in Fig. 6(b) and (d) present that most experimental data fall on a straight line in the frequency range covered, which indicates
that the conductivity has main contribution to ε [18]. With the decreasing temperature, the data points of ε deviate from the straight line at T < 210 K. This phenomenon is the condensation of the polarized clusters. Owing to the condensation of small clusters, the size of microdomains increase, in which the slow dynamics of the domain walls contribute to the delay of the response to the external alternating field, particularly at high frequencies [19]. 4. Conclusion In summary, by doping Ga ion into TMO, the prominent changes are observed in dielectric constants and loss tangent of the ten TMO samples. Two dielectric plateaus appear at lower and higher temperatures respectively, between which the dielectric constants boost steeply, and accompanied by a peak in the loss tangent. It is quite different with the parent TMO that the dielectric loss
320
J. Xu, Y. Cui / Materials Science and Engineering B 178 (2013) 316–320
of Tb1−x Gax MnO3 is low in a wide temperature range even at room temperature. XRD patterns indicate that the doping with high Ga content are difficult in TbMnO3 . And compared with TbGay Mn1−y O3 , Tb1−x Gax MnO3 samples have larger grains, which may contributed to the larger dielectric constants and higher switching temperatures. The curves of ε with frequency fall on a straight line at T > 210 K, which indicating that the conductivity has main contribution to the electrical processes. Acknowledgement We acknowledge the financial support from National Natural Science Foundation of China (No. 10975013). References [1] S. Jin, T.H. Tiefel, M. McCormack, R.A. Fastnacht, R. Ramesh, L.H. Chen, Science 264 (1993) 413. [2] A. Asamitsu, Y. Moritomo, Y. Tomioka, T. Arima, Y. Tokura, Nature (London) 373 (1995) 407. [3] A. Tiwari, K.P. Rajeev, J. Narayan, Solid State Communications 121 (2002) 357. [4] T. Kimura, T. Goto, H. Shintani, K. Ishizaka, T. Arima, Y. Tokura, Nature 426 (2003) 55.
[5] T. Goto, T. Kimura, G. Lawes, A.P. Ramirez, Y. Tokura, Physical Review Letters 92 (2004) 257201. [6] Y.M. Cui, Y.F. Tian, W. Liu, Y.F. Li, R.M. Wang, T. Wu, AIP Advances 1 (2011) 042129. [7] C.C. Yang, M.K. Chung, W.H. Li, T.S. Chan, R.S. Liu, Y.H. Lien, C.Y. Huang, Y.Y. Chan, Y.D. Yao, J.W. Lynn, Physical Review B 74 (2006) 094409. [8] Y.M. Cui, Physica B 403 (2008) 2963. [9] F. Pérez, J. Heiras, R. Escudero, Physica Status Solidi (c) 4 (2007) 4049. [10] J. Blasco, C. Ritter, J. García, J.M. de Teresa, J. Pérez-Cacho, M.R. Ibarra, Physical Review B 62 (2000) 5609. [11] N. Mufti, A.A. Nugroho, G.R. Blake, T.T.M. Palstra, Physical Review B 78 (2008) 024109. [12] T. Kimura, G. Lawes, T. Goto, Y. Tokura, A.P. Ramirez, Physical Review B 71 (2005) 224425. [13] J.A. Alonso, M.J. Martinez-Lope, M.T. Casais, M.T. Fernandez-Diaz, Inorganic Chemistry 39 (2000) 917. [14] T. Goto, Y. Yamasaki, H. Watanable, T. Kimura, Y. Tokura, Physical Review B 72 (2005) 220703. [15] A. Pimenov, A.A. Mukhin, V. Yu Ivanov, V.D. Travkin, A.M. Balbashov, A. Loidl, Nature Physics 2 (2006) 97. [16] H. Luo, R. Jing, Y.M. Cui, H.L. Wang, R.M. Wang, Progress in Natural Science: Materials International 20 (2010) 111. [17] J.B. Wu, C.W. Nan, Y.H. Lin, Y. Deng, Physical Review Letters 89 (2004) 217601. [18] Y.M. Cui, L.W. Liu, G.L. Xie, R.M. Wang, Solid State Communications 138 (2006) 481. [19] C.C. Wang, Y.M. Cui, G.L. Xie, C.P. Chen, L.W. Zhang, Physical Review B 72 (2005) 064513.