- Email: [email protected]
Phase transition in ZnSe at high pressures and high temperatures
Journal of Physics and Chemistry of Solids 141 (2020) 109409
Contents lists available at ScienceDirect
Journal of Physics and Chemistry of Solids journal homepage: http://www.elsevier.com/locate/jpcs
Phase transition in ZnSe at high pressures and high temperatures Shigeaki Ono Research Institute for Marine Geodynamics, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka-shi, Kanagawa, 237-0061, Japan
A R T I C L E I N F O
A B S T R A C T
Keywords: Inorganic compounds High pressure X-ray diffraction Phase transitions
The phase transition boundary between the zinc blende and the rock-salt structure in zinc selenide (ZnSe) was determined using high-pressure experiments combined with the synchrotron X-ray diffraction technique. Sig nificant hysteresis in the phase transition was not observed at high temperatures. The transition pressure was extrapolated to be 13.3 GPa at 300 K, and the dP/dT slope of the phase boundary had a negative dependence of 0.0033 GPa/T. As this transition pressure was used as the pressure standard in the high-pressure experiments, the new value influences a wide range of high-pressure science. This negative dependence is similar to those of semiconductor–metal transitions, such as ZnS, GaAs, and GaP. We found a linear relationship between the semiconductor–metal transition pressures and dP/dT slopes in II–VI and III–V compounds.
1. Introduction
from the zinc blende to the rock-salt structure at high temperatures, because the influences of transition kinetics and differential stress on the phase transition are known to decrease with an increase in temperature.
The semiconducting II–VI and III–V compounds are of great interest to industry due to their wide band gaps. Pressure-induced phase tran sitions from semiconductor to metal states are also of interest in highpressure science, since they are used as the fixed-points for static pres sure calibration curves. Zinc chalcogenides, such as zinc selenide (ZnSe) and zinc sulfide (ZnS), have cubic zinc-blende-type structures under ambient conditions. The phase transition from the zinc blende (fourfoldcoordinated) to the rock-salt type (sixfold-coordinated) is accompanied by a drastic drop in the electrical resistivity. The behavior of ZnSe under high pressure has been the subject of many experimental and theoretical studies [1–16]. The phase transition of ZnSe from zinc blende to rock-salt structure is reported to occur at around 13 GPa [2–7,9,11,12, 15]. Recent experiments using Raman spectroscopy reported a discon tinuity in the TO and LO modes in the zinc blende structure at ~5 GPa [6,11]. Lin et al. [11] also reported a similar anomaly at 9.1 GPa. In contrast, a phase transition from the rock-salt into the cinnabar structure was observed on decompression [13,14]. Theoretical studies have confirmed that the phase transition from zinc blende to rock-salt struc ture occurs at pressures of 10–15 GPa [7,10,15]. Although previous studies have improved the understanding of the pressure-induced tran sition sequence of ZnSe, the anomalies in the zinc blende structure at 5 and 9 GPa and the stability of the cinnabar structure are still not un derstood. Since most previous experiments have been performed at room temperature, these observations might be related to the transition kinetics and the differential stress in the sample. Taking into account these factors, the aim in this work is to investigate the phase transition
2. Methods Experiments were performed using a hydrothermal diamond anvil cell, described in detail by Bassett et al. [17]. Temperature was measured by chromel–alumel (Type K) thermocouples accurate to �1.5 � C. The junctions of thermocouples were placed on the anvils, which were heated using molybdenum wire heaters. The temperature was controlled by adjusting the power supply, and the fluctuation of tem perature during measurements was within 1–3 � C. Powdered ZnSe (99.99% purity) with zinc blende structure was used as the starting material. The lattice parameter of this sample measured by the X-ray diffraction method was a ¼ 5.6683(4) Å under ambient conditions. The starting materials were compressed in the diamond anvil cell using diamonds with 300 or 450 μm diameter culet. The sample chamber consisted of a 50–100 μm hole drilled in a rhenium gasket, preindented to a thickness of around 50 μm. The sample was loaded with pellets of NaCl powder serving as a quasihydrostatic pressuretransmitting medium. The NaCl powder was also used as a pressure calibrant. Conventional angle-dispersive X-ray diffraction was used at the synchrotron beamline, at the AR-NE1A at KEK (Japan) [18]. The X-ray diffraction patterns were obtained on an imaging plate system (Rigaku) of size 3000 � 3000 pixels. The distance between the sample and the imaging plate was ~320 mm. The X-ray wavelength was calibrated
E-mail address: [email protected]. https://doi.org/10.1016/j.jpcs.2020.109409 Received 27 September 2019; Received in revised form 12 February 2020; Accepted 13 February 2020 Available online 14 February 2020 0022-3697/© 2020 The Author. Published by Elsevier Ltd. This is an open access (http://creativecommons.org/licenses/by-nc-nd/4.0/).
article
under
the
CC
BY-NC-ND
license
S. Ono
Journal of Physics and Chemistry of Solids 141 (2020) 109409
Fig. 2. Examples of the observed X-ray diffraction patterns for the phase transition with changing temperature. Diffraction peaks are labeled as follows: Z – zinc blende phase; R – rock-salt phase. Numbers on labels correspond to the indices of the cubic symmetry. (a) Diffraction peaks of the zinc blende structure decrease (down arrows) with a temperature increase from 400 to 600 K, and those of the rock-salt structure appear (up arrows); (b) diffraction peaks of the rock-salt structure decrease (down arrows) with a temperature decrease from 600 to 400 K, and those of the zinc blende structure appear (up arrows).
Fig. 1. Examples of the observed X-ray diffraction patterns at room tempera ture. Upper image: zinc blende phase at 10.5 GPa; lower image: rock-salt phase at 25.4 GPa. Diffraction peaks are labeled as follows: Z – zinc blende phase; R – rock-salt phase; S B1-type NaCl. Numbers on labels correspond to the indices of the cubic symmetry. Wavelength of the monochromatic incident X-ray beam was λ ¼ 0.4179 Å.
using a CeO2 standard. The X-ray beam size was collimated to a diameter of about 30 μm. The observed intensities on the imaging plate were converted into a conventional 2θ-intensity diffraction pattern. The sample pressure was determined from the unit cell volume of NaCl using the equation of state for NaCl [19]. The sample was first compressed at room temperature before the Xray diffraction measurement. After the pressure reached the target value, which was confirmed by Raman spectra of the culet face of the diamond anvil [20], the temperature of the sample was increased, and the X-ray diffraction data from the sample were acquired. These data were acquired in the range of 300–900 K at fixed-pressure loads. 3. Results Experimental runs were carried out at pressures of up to 25 GPa; and at each pressure increment, the cell was screwed to hold the sample pressure. Initially, the X-ray diffraction data were acquired at room temperature. Typical diffraction data at 10.5 and 25.4 GPa are shown in Fig. 1. The zinc blende structure of the starting material was observed at 10.5 GPa. When the pressure was increased to around 25.4 GPa, the rock-salt structure was observed, indicating that the phase transition from zinc blende to rock-salt structure occurred with increasing pres sure. Previous studies reported that the phase transition was observed at 11–18 GPa, which is in general agreement with the present experimental results. Next, high-temperature experiments were performed to 900 K. The changes in the X-ray diffraction patterns at the phase transition at high temperatures are shown in Fig. 2. The force on the anvils was adjusted by turning the driver screws to maintain the target pressure. However, the pressure slightly increased as the result of thermal expansivity or decreased as the result of volume change of the phase transition or
Fig. 3. Experimental results for the transition boundary of ZnSe. Open and solid circles denote the stability conditions for the zinc blende and rock-salt structures, respectively. The dashed line and the open and solid circles were experimentally determined based on the extrapolation of the hightemperature observations to 300 K.
thermal relaxation of the gasket. The zinc blende structure was stable at 400 K and ~12 GPa, and the intensities of the peaks for the zinc blende structure decreased as the temperature was increased to 600 K, and peaks from the rock-salt structure appeared at 600 K (Fig. 2a). This 2
S. Ono
Journal of Physics and Chemistry of Solids 141 (2020) 109409
Table 1 The transition pressure of ZnSe at room temperature from the literature and from this study. P (GPa)
Method
Reference
18.0 13.7 14.6 13.0 11.8–14.5 13.0 14.4 13.6 12.1 10.8 13.3
X-ray diffraction Optical observation Shock experiment Resistivity X-ray diffraction X-ray diffraction Raman spectra Shock experiment X-ray diffraction Calculation X-ray diffraction
[1] [2] [4] [5] [6] [9] [11] [12] [14] [15] This study
Table 2 Comparison of the phase boundaries between the semiconducting–metallic transitions. a GaP GaAs ZnS ZnSe
22.6 18.0 14.4 13.2
b
References 0.0014 0.0025 0.0033 0.0033
[18] [21] [22] This study
The parameters are given by P(GPa) ¼ a þ b � T(K), where T and P are tem perature (K) and pressure (GPa), respectively.
indicated that the rock-salt structure was stable at 600 K and ~12 GPa. The reverse transition from the rock-salt to the zinc blende structure was observed with a decrease in temperature (Fig. 2b). Significant hysteresis in the transition pressure was not observed at high temperatures. The transition boundary was determined by the acquired X-ray diffraction data. The pressure–temperature conditions for the stable structures identified are shown in Fig. 3. The transition pressure at room temperature was 13.3 GPa, and the dP/dT slope of the phase boundary was negative. The transition boundary shown in Fig. 3 is represented by the linear equation: P (GPa) ¼ 14.2(2)
0.0033(2) � T (K)
The transition pressure at room temperature was determined using an extrapolation of the high-temperature data. This value is in general agreement with results reported in previous studies (Table 1). The dP/dT slope determined in this study is consistent with that reported by Kusaba and Kikegara [14], although their value of transition pressure was 1.2 GPa lower than that determined in the present study.
Fig. 4. Gradient of dP/dT slope versus transition pressure. The values of transition pressures are at room temperature. The dP/dT gradients represent the phase transition boundaries in GaP, GaAs, ZnS, and ZnSe.
4. Discussion Pellicer-Porres et al. [13] reported the formation of a cinnabar structure with a decrease in pressure from the rock-salt structure. An ab-initio calculation also suggested that the cinnabar structure was stable within a narrow range of pressures (10.2–13.4 GPa) [10]. In the present study, the cinnabar structure was not observed, since X-ray diffraction data were not acquired while the pressure was reduced. This hysteresis is likely to be related to transition kinetics. Kusaba and Kikegawa [14] reported that the rock-salt structure directly transforms into the zinc blende structure above 573 K, which is in good agreement with our observations. Table 1 shows a comparison between the transition pressures found in previous studies and the present results. The values of pressure vary widely, within 10–18 GPa, for several reasons. Firstly, high-pressure experiments using the quench method require the pressure calibration in order to estimate the experimental pressure. Although several cali brant points were used in the quench experiments, the differences in pressure calibration may have influenced the pressure determination, and some calibration points may have significant uncertainty, especially since these studies were performed before the 1970s. Secondly, it is known that a compression-related differential stress accumulates at room temperature, and effects of differential stress on the transition pressure are often observed in studies of phase transition at high pres sures. Different stress conditions are expected for different experimental methods, meaning that the inconsistency in transition pressures is determined by the room-temperature compression. However, the in fluence of differential stress was not likely to be significant in the present study, since the phase boundary was determined using high-temperature data. Table 2 shows the transition boundaries between the semiconductor-
and metal-phases in II–VI and III–V compounds. All dP/dT slopes had negative values, and the transition pressures were higher for III–V than for II–VI compounds. The relationships between the transition pressures and dP/dT slopes are shown in Fig. 4, and can be approximated by linear relationships. It is known that the ionic bonding nature of the II–VI compound semiconductors is significant compared with that of the III–V compound semiconductors, suggesting that this linear relationship is due to an increase in the ionic bonding nature in the semiconductor compounds. 5. Conclusions The phase transition in ZnSe was investigated using a diamond anvil cell at temperatures and pressures up to 900 K and 25 GPa, respectively. The transition pressure between the zinc blende and rock-salt structures decreased as the temperature increased. The room-temperature transi tion pressure, which is often used in the pressure calibration in highpressure experiments, was estimated to be 13.3 GPa. Since no signifi cant hysteresis in the phase transition was observed at high tempera tures, the transition pressure determined in this study is suitable for the pressure standard in high-pressure experiments. Funding This work was partially supported by Japan Society for the Promo tion of Science, Grant Numbers JP18K03792 and JP16H02742.
3
S. Ono
Journal of Physics and Chemistry of Solids 141 (2020) 109409
Declaration of competing interest
[8] M.I. McMahon, R.J. Nelmes, New structural systematics in the II-VI, III-V, and group-IV semiconductors at high pressure, Phys. Status Solidi 198 (1996) 389–402. [9] H. Karzel, W. Potzel, M. K€ offerlein, W. Schiessl, M. Steiner, U. Hiller, G.M. Kalvius, D.W. Mitchell, T.P. Das, P. Blaha, K. Schwarz, M.P. Pasternak, Lattice dynamics and hyperfine interactions in ZnO and ZnSe at high external pressure, Phys. Rev. B 53 (1996) 11425–11438. [10] M. C^ ot�e, O. Zakharov, A. Rubio, M.L. Cohen, Ab initio calculations of the pressureinduced structural phase transitions for four II-VI compounds, Phys. Rev. B 55 (1997) 13025–13031. [11] C.M. Lin, D.S. Chuu, T.J. Yang, W.C. Chou, J. Xu, E. Huang, Raman spectroscopy study of ZnSe and Zn0.84Fe0.16Se at high pressures, Phys. Rev. B 55 (1997) 13641–13646. [12] M. Uchino, T. Mashimo, Measurement of hugoniot-compression curve of ZnSe, Rev. High. Pres Sci. Technol. 7 (1998) 835–837. [13] J. Pellicer-Porres, A. Segura, V. Mu~ noz, J. Zú~ niga, J.P. Iti�e, A. Polian, P. Munsch, Cinnabar phase in ZnSe at high pressure, Phys. Rev. B 65 (2001), 012109. [14] K. Kusaba, T. Kikegawa, A new high-pressure phase of ZnSe with B9-type structure, J. Phys. Chem. Solid. 63 (2002) 651–655. [15] M. Durandurdu, The structural phase transition of ZnSe under hydrostatic and nonhydrostatic compressions: an ab initio molecular dynamics study, J. Phys. Condens. Matter 21 (2009) 125403, https://doi.org/10.1088/0953-8984/21/12/ 125403. [16] L.A. Valdez, M.A. Caravaca, R.A. Casali, Ab-initio study of elastic anisotropy, hardness and volumetric thermal expansion coefficient of ZnO, ZnS, ZnSe in wurtzite and zinc blende phases, J. Phys. Chem. Solid. 134 (2019) 245–254, https://doi.org/10.1016/j.jpcs.2019.05.019. [17] W.A. Bassett, A.H. Shen, M. Bucknum, I.-M. Chou, A new diamond anvil cell for hydrothermal studies to 2.5 GPa and from 190 to 1200 � C, Rev. Sci. Instrum. 64 (1993) 2340–2345. [18] S. Ono, T. Kikegawa, Determination of the phase boundary of GaP using in situ high pressure and high-temperature X-ray diffraction, High Pres. Res. 37 (2017) 28–35, https://doi.org/10.1080/08957959.2016.1269900. [19] P.I. Dorogokupets, A. Dewaele, Equations of state of MgO, Au, Pt, NaCl-B1, and NaCl-B2: internally consistent high-temperature pressure scales, High Pres. Res. 27 (2007) 431–446, https://doi.org/10.1080/08957950701659700. [20] S. Ono, K. Mibe, Y. Ohishi, Raman spectra of culet face of diamond anvils and application as optical pressure sensor to high temperatures, J. Appl. Phys. 116 (2014), 053517, https://doi.org/10.1063/1.4891681. [21] S. Ono, T. Kikegawa, Phase transformation of GaAs at high pressures and temperatures, J. Phys. Chem. Solid. 113 (2018) 1–4, https://doi.org/10.1016/j. jpcs.2017.10.005. [22] S. Ono, T. Kikegawa, Determination of the phase boundary of ZnS, Phase Transitions 91 (2018) 9–14, https://doi.org/10.1080/01411594.2017.1350958.
The author declares no conflict of interest. CRediT authorship contribution statement Shigeaki Ono: Writing - original draft, Conceptualization, Method ology, Data curation. Acknowledgments The synchrotron radiation experiments were performed at the PFAR, High Energy Accelerator Research Organization, Japan (Proposal Nos. 2017G056 and 2019G003). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.jpcs.2020.109409. References [1] P.L. Smith, J.E. Martin, The high-pressure structures of zinc sulphide and zinc selenide, Phys. Lett. 19 (1965) 541–543. [2] G.J. Piermarini, S. Block, Ultrahigh pressure diamond-anvil cell and several semiconductor phase transition pressure in relation to the fixed point pressure scale, Rev. Sci. Instrum. 46 (1975) 973–979. [3] B.A. Weinstein, Phonon dispersion of zinc chalcogenides under extreme pressure and the metallic transformation, Solid State Commun. 26 (1977) 595–598. [4] W.H. Gust, Shock induced transition stresses for zinc sulfide and zinc selenide, J. Appl. Phys. 53 (1982) 4843–4846. [5] S.R. Tiong, M. Hiramatsu, Y. Matsushima, E. Ito, The phase transition pressure of zincsulfoselenide single crystal, Jpn. J. Appl. Phys. 28 (1989) 291–292. [6] R.G. Greene, H. Luo, A.L. Ruoff, High pressure X-ray and Raman study of ZnSe, J. Phys. Chem. Solid. 56 (1995) 521–524. [7] V.I. Smelyansky, J.S. Tse, Theoretical study on the high-pressure phase transformation in ZnSe, Phys. Rev. B 52 (1995) 4658–4661.
4
Contents lists available at ScienceDirect
Journal of Physics and Chemistry of Solids journal homepage: http://www.elsevier.com/locate/jpcs
Phase transition in ZnSe at high pressures and high temperatures Shigeaki Ono Research Institute for Marine Geodynamics, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka-shi, Kanagawa, 237-0061, Japan
A R T I C L E I N F O
A B S T R A C T
Keywords: Inorganic compounds High pressure X-ray diffraction Phase transitions
The phase transition boundary between the zinc blende and the rock-salt structure in zinc selenide (ZnSe) was determined using high-pressure experiments combined with the synchrotron X-ray diffraction technique. Sig nificant hysteresis in the phase transition was not observed at high temperatures. The transition pressure was extrapolated to be 13.3 GPa at 300 K, and the dP/dT slope of the phase boundary had a negative dependence of 0.0033 GPa/T. As this transition pressure was used as the pressure standard in the high-pressure experiments, the new value influences a wide range of high-pressure science. This negative dependence is similar to those of semiconductor–metal transitions, such as ZnS, GaAs, and GaP. We found a linear relationship between the semiconductor–metal transition pressures and dP/dT slopes in II–VI and III–V compounds.
1. Introduction
from the zinc blende to the rock-salt structure at high temperatures, because the influences of transition kinetics and differential stress on the phase transition are known to decrease with an increase in temperature.
The semiconducting II–VI and III–V compounds are of great interest to industry due to their wide band gaps. Pressure-induced phase tran sitions from semiconductor to metal states are also of interest in highpressure science, since they are used as the fixed-points for static pres sure calibration curves. Zinc chalcogenides, such as zinc selenide (ZnSe) and zinc sulfide (ZnS), have cubic zinc-blende-type structures under ambient conditions. The phase transition from the zinc blende (fourfoldcoordinated) to the rock-salt type (sixfold-coordinated) is accompanied by a drastic drop in the electrical resistivity. The behavior of ZnSe under high pressure has been the subject of many experimental and theoretical studies [1–16]. The phase transition of ZnSe from zinc blende to rock-salt structure is reported to occur at around 13 GPa [2–7,9,11,12, 15]. Recent experiments using Raman spectroscopy reported a discon tinuity in the TO and LO modes in the zinc blende structure at ~5 GPa [6,11]. Lin et al. [11] also reported a similar anomaly at 9.1 GPa. In contrast, a phase transition from the rock-salt into the cinnabar structure was observed on decompression [13,14]. Theoretical studies have confirmed that the phase transition from zinc blende to rock-salt struc ture occurs at pressures of 10–15 GPa [7,10,15]. Although previous studies have improved the understanding of the pressure-induced tran sition sequence of ZnSe, the anomalies in the zinc blende structure at 5 and 9 GPa and the stability of the cinnabar structure are still not un derstood. Since most previous experiments have been performed at room temperature, these observations might be related to the transition kinetics and the differential stress in the sample. Taking into account these factors, the aim in this work is to investigate the phase transition
2. Methods Experiments were performed using a hydrothermal diamond anvil cell, described in detail by Bassett et al. [17]. Temperature was measured by chromel–alumel (Type K) thermocouples accurate to �1.5 � C. The junctions of thermocouples were placed on the anvils, which were heated using molybdenum wire heaters. The temperature was controlled by adjusting the power supply, and the fluctuation of tem perature during measurements was within 1–3 � C. Powdered ZnSe (99.99% purity) with zinc blende structure was used as the starting material. The lattice parameter of this sample measured by the X-ray diffraction method was a ¼ 5.6683(4) Å under ambient conditions. The starting materials were compressed in the diamond anvil cell using diamonds with 300 or 450 μm diameter culet. The sample chamber consisted of a 50–100 μm hole drilled in a rhenium gasket, preindented to a thickness of around 50 μm. The sample was loaded with pellets of NaCl powder serving as a quasihydrostatic pressuretransmitting medium. The NaCl powder was also used as a pressure calibrant. Conventional angle-dispersive X-ray diffraction was used at the synchrotron beamline, at the AR-NE1A at KEK (Japan) [18]. The X-ray diffraction patterns were obtained on an imaging plate system (Rigaku) of size 3000 � 3000 pixels. The distance between the sample and the imaging plate was ~320 mm. The X-ray wavelength was calibrated
E-mail address: [email protected]. https://doi.org/10.1016/j.jpcs.2020.109409 Received 27 September 2019; Received in revised form 12 February 2020; Accepted 13 February 2020 Available online 14 February 2020 0022-3697/© 2020 The Author. Published by Elsevier Ltd. This is an open access (http://creativecommons.org/licenses/by-nc-nd/4.0/).
article
under
the
CC
BY-NC-ND
license
S. Ono
Journal of Physics and Chemistry of Solids 141 (2020) 109409
Fig. 2. Examples of the observed X-ray diffraction patterns for the phase transition with changing temperature. Diffraction peaks are labeled as follows: Z – zinc blende phase; R – rock-salt phase. Numbers on labels correspond to the indices of the cubic symmetry. (a) Diffraction peaks of the zinc blende structure decrease (down arrows) with a temperature increase from 400 to 600 K, and those of the rock-salt structure appear (up arrows); (b) diffraction peaks of the rock-salt structure decrease (down arrows) with a temperature decrease from 600 to 400 K, and those of the zinc blende structure appear (up arrows).
Fig. 1. Examples of the observed X-ray diffraction patterns at room tempera ture. Upper image: zinc blende phase at 10.5 GPa; lower image: rock-salt phase at 25.4 GPa. Diffraction peaks are labeled as follows: Z – zinc blende phase; R – rock-salt phase; S B1-type NaCl. Numbers on labels correspond to the indices of the cubic symmetry. Wavelength of the monochromatic incident X-ray beam was λ ¼ 0.4179 Å.
using a CeO2 standard. The X-ray beam size was collimated to a diameter of about 30 μm. The observed intensities on the imaging plate were converted into a conventional 2θ-intensity diffraction pattern. The sample pressure was determined from the unit cell volume of NaCl using the equation of state for NaCl [19]. The sample was first compressed at room temperature before the Xray diffraction measurement. After the pressure reached the target value, which was confirmed by Raman spectra of the culet face of the diamond anvil [20], the temperature of the sample was increased, and the X-ray diffraction data from the sample were acquired. These data were acquired in the range of 300–900 K at fixed-pressure loads. 3. Results Experimental runs were carried out at pressures of up to 25 GPa; and at each pressure increment, the cell was screwed to hold the sample pressure. Initially, the X-ray diffraction data were acquired at room temperature. Typical diffraction data at 10.5 and 25.4 GPa are shown in Fig. 1. The zinc blende structure of the starting material was observed at 10.5 GPa. When the pressure was increased to around 25.4 GPa, the rock-salt structure was observed, indicating that the phase transition from zinc blende to rock-salt structure occurred with increasing pres sure. Previous studies reported that the phase transition was observed at 11–18 GPa, which is in general agreement with the present experimental results. Next, high-temperature experiments were performed to 900 K. The changes in the X-ray diffraction patterns at the phase transition at high temperatures are shown in Fig. 2. The force on the anvils was adjusted by turning the driver screws to maintain the target pressure. However, the pressure slightly increased as the result of thermal expansivity or decreased as the result of volume change of the phase transition or
Fig. 3. Experimental results for the transition boundary of ZnSe. Open and solid circles denote the stability conditions for the zinc blende and rock-salt structures, respectively. The dashed line and the open and solid circles were experimentally determined based on the extrapolation of the hightemperature observations to 300 K.
thermal relaxation of the gasket. The zinc blende structure was stable at 400 K and ~12 GPa, and the intensities of the peaks for the zinc blende structure decreased as the temperature was increased to 600 K, and peaks from the rock-salt structure appeared at 600 K (Fig. 2a). This 2
S. Ono
Journal of Physics and Chemistry of Solids 141 (2020) 109409
Table 1 The transition pressure of ZnSe at room temperature from the literature and from this study. P (GPa)
Method
Reference
18.0 13.7 14.6 13.0 11.8–14.5 13.0 14.4 13.6 12.1 10.8 13.3
X-ray diffraction Optical observation Shock experiment Resistivity X-ray diffraction X-ray diffraction Raman spectra Shock experiment X-ray diffraction Calculation X-ray diffraction
[1] [2] [4] [5] [6] [9] [11] [12] [14] [15] This study
Table 2 Comparison of the phase boundaries between the semiconducting–metallic transitions. a GaP GaAs ZnS ZnSe
22.6 18.0 14.4 13.2
b
References 0.0014 0.0025 0.0033 0.0033
[18] [21] [22] This study
The parameters are given by P(GPa) ¼ a þ b � T(K), where T and P are tem perature (K) and pressure (GPa), respectively.
indicated that the rock-salt structure was stable at 600 K and ~12 GPa. The reverse transition from the rock-salt to the zinc blende structure was observed with a decrease in temperature (Fig. 2b). Significant hysteresis in the transition pressure was not observed at high temperatures. The transition boundary was determined by the acquired X-ray diffraction data. The pressure–temperature conditions for the stable structures identified are shown in Fig. 3. The transition pressure at room temperature was 13.3 GPa, and the dP/dT slope of the phase boundary was negative. The transition boundary shown in Fig. 3 is represented by the linear equation: P (GPa) ¼ 14.2(2)
0.0033(2) � T (K)
The transition pressure at room temperature was determined using an extrapolation of the high-temperature data. This value is in general agreement with results reported in previous studies (Table 1). The dP/dT slope determined in this study is consistent with that reported by Kusaba and Kikegara [14], although their value of transition pressure was 1.2 GPa lower than that determined in the present study.
Fig. 4. Gradient of dP/dT slope versus transition pressure. The values of transition pressures are at room temperature. The dP/dT gradients represent the phase transition boundaries in GaP, GaAs, ZnS, and ZnSe.
4. Discussion Pellicer-Porres et al. [13] reported the formation of a cinnabar structure with a decrease in pressure from the rock-salt structure. An ab-initio calculation also suggested that the cinnabar structure was stable within a narrow range of pressures (10.2–13.4 GPa) [10]. In the present study, the cinnabar structure was not observed, since X-ray diffraction data were not acquired while the pressure was reduced. This hysteresis is likely to be related to transition kinetics. Kusaba and Kikegawa [14] reported that the rock-salt structure directly transforms into the zinc blende structure above 573 K, which is in good agreement with our observations. Table 1 shows a comparison between the transition pressures found in previous studies and the present results. The values of pressure vary widely, within 10–18 GPa, for several reasons. Firstly, high-pressure experiments using the quench method require the pressure calibration in order to estimate the experimental pressure. Although several cali brant points were used in the quench experiments, the differences in pressure calibration may have influenced the pressure determination, and some calibration points may have significant uncertainty, especially since these studies were performed before the 1970s. Secondly, it is known that a compression-related differential stress accumulates at room temperature, and effects of differential stress on the transition pressure are often observed in studies of phase transition at high pres sures. Different stress conditions are expected for different experimental methods, meaning that the inconsistency in transition pressures is determined by the room-temperature compression. However, the in fluence of differential stress was not likely to be significant in the present study, since the phase boundary was determined using high-temperature data. Table 2 shows the transition boundaries between the semiconductor-
and metal-phases in II–VI and III–V compounds. All dP/dT slopes had negative values, and the transition pressures were higher for III–V than for II–VI compounds. The relationships between the transition pressures and dP/dT slopes are shown in Fig. 4, and can be approximated by linear relationships. It is known that the ionic bonding nature of the II–VI compound semiconductors is significant compared with that of the III–V compound semiconductors, suggesting that this linear relationship is due to an increase in the ionic bonding nature in the semiconductor compounds. 5. Conclusions The phase transition in ZnSe was investigated using a diamond anvil cell at temperatures and pressures up to 900 K and 25 GPa, respectively. The transition pressure between the zinc blende and rock-salt structures decreased as the temperature increased. The room-temperature transi tion pressure, which is often used in the pressure calibration in highpressure experiments, was estimated to be 13.3 GPa. Since no signifi cant hysteresis in the phase transition was observed at high tempera tures, the transition pressure determined in this study is suitable for the pressure standard in high-pressure experiments. Funding This work was partially supported by Japan Society for the Promo tion of Science, Grant Numbers JP18K03792 and JP16H02742.
3
S. Ono
Journal of Physics and Chemistry of Solids 141 (2020) 109409
Declaration of competing interest
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The author declares no conflict of interest. CRediT authorship contribution statement Shigeaki Ono: Writing - original draft, Conceptualization, Method ology, Data curation. Acknowledgments The synchrotron radiation experiments were performed at the PFAR, High Energy Accelerator Research Organization, Japan (Proposal Nos. 2017G056 and 2019G003). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.jpcs.2020.109409. References [1] P.L. Smith, J.E. Martin, The high-pressure structures of zinc sulphide and zinc selenide, Phys. Lett. 19 (1965) 541–543. [2] G.J. Piermarini, S. Block, Ultrahigh pressure diamond-anvil cell and several semiconductor phase transition pressure in relation to the fixed point pressure scale, Rev. Sci. Instrum. 46 (1975) 973–979. [3] B.A. Weinstein, Phonon dispersion of zinc chalcogenides under extreme pressure and the metallic transformation, Solid State Commun. 26 (1977) 595–598. [4] W.H. Gust, Shock induced transition stresses for zinc sulfide and zinc selenide, J. Appl. Phys. 53 (1982) 4843–4846. [5] S.R. Tiong, M. Hiramatsu, Y. Matsushima, E. Ito, The phase transition pressure of zincsulfoselenide single crystal, Jpn. J. Appl. Phys. 28 (1989) 291–292. [6] R.G. Greene, H. Luo, A.L. Ruoff, High pressure X-ray and Raman study of ZnSe, J. Phys. Chem. Solid. 56 (1995) 521–524. [7] V.I. Smelyansky, J.S. Tse, Theoretical study on the high-pressure phase transformation in ZnSe, Phys. Rev. B 52 (1995) 4658–4661.
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