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Structure and Lattice Dynamics of Calcium Chalcogenides under High Pressure
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 5 (2018) 18874–18878
www.materialstoday.com/proceedings
ICMPC_2018
Structure and Lattice Dynamics of Calcium Chalcogenides under High Pressure S. C. Rakesh Roshana, Lavanya Kunduruab, N. Yedukondalua*, and M. Sainatha a
Rajiv Gandhi University of Knowledge Technologies, RGUKT Basar, 504107, India b jntu hyderabad
Abstract We have investigated the structural and lattice dynamics of alkaline-earth chalcogenides namely CaX (X = S, Se Te) compounds under high pressure up to 50 GPa using plane wave pseudo potential approach based on density functional theory. It is found that CaS, CaSe and CaTe compounds undergo first order structural phase transitions from NaCl-type (B1) to CsCl-type (B2) phase at 34.9, 31.8 and 24.2 GPa respectively and the obtained transitions pressures are consistent with the experimental results. We have also calculated the phonon dispersions of these three compounds in B1 phase and are found to be dynamically stable even after the phase transition pressure to maximum pressure of the present study (50 GPa) for CaS, CaSe whereas CaTe is stable up to 30 GPa. © 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of Materials Processing and characterization. Keywords: Phonon dispersion;Density Fumctional Theory;
1. Introduction Calcium chalcogenide CaX (X = S, Se, and Te) compounds belong to the class of alkaline-earth chalcogenides. In one hand, they have been the subject of considerable interest from both theoretical and experimental perspective due to their technological applications in the fields of microelectronics, infrared-sensitive devices and luminescence1,2.
* Corresponding author. Tel.+91-9908797832 E-mail address: [email protected]
2214-7853 © 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of Materials Processing and characterization.
S. C. Rakesh Roshan et al./ Materials Today: Proceedings 5 (2018) 18874–18878
18875
On the other hand, high pressure research on structural phase transformations based on the theoretical calculations or measurements have become quite interesting in recent years, as they provide good insights in designing novel materials with specified properties at extreme conditions. Calcium chalcogenides possess rock-salt NaCl-type (B1) structure at ambient conditions and they transform to CsCl-type (B2) structure under application of hydrostatic pressure. These are closed shell ionic systems and have similar electronic structures and physical properties3. Structural studies of CaS, CaSe and CaTe under high pressure up to 52 GPa, have been carried out experimentally using x-ray diffraction technique and observe first order structural phase transitions from B1B2 phase4. The structural phase transitions are associated with many changes related to properties of the system from micro- to macroscopic level. Also, lattice dynamical calculations play a key role in determining the dynamical stability of materials at ambient as well as at high pressure. First principles calculations based on density functional theory (DFT) is a powerful tool to investigate pressure dependent structural and lattice dynamical properties of materials. In the present study, we have systematically investigated the pressure induced structural phase transitions and lattice dynamical properties of three calcium chalcogenides. 1.1. Computational details All the first principles calculations were carried out using plane wave pseudo potential approach implemented quantum espresso package5. Norm conserving pseudo potentials are used to treat the electron-ion interactions whereas electron-electron interactions are treated within generalized gradient approximation with Perdew-BurkeErnzerhof parameterization. The plane wave cutoff energy was set to 100 Ry and a k-mesh of 8×8×8 using Monkhorst-Pack grid scheme. Lattice dynamical properties were calculated using density functional perturbation theory (DFPT). Eight dynamical matrices were calculated using 4x4x4 q-mesh and are interpolated to compute the phonon spectra of the CaX compounds. 2. Results and Discussion 2.1 Structural phase transitions in CaX (S, Se, Te) compounds High pressure studies using first principles calculations provide deep insight for predicting novel phases of materials under high pressure for diverse applications. CaX compounds are simple binary systems to understand the structural phase transitions and their dynamical stability under high pressure. By considering the experimental data as input, we first optimized the lattice geometry of three investigated CaX compounds at ambient as well as at high pressure up to 50 GPa in both B1 and B2 phases. As illustrated in figure 1a, c & e, the calculated enthalpy as a function of pressure shows the CaS, CaSe and CaTe compounds undergo a structural phase transitions from B1 to B2 phase transitions at 34.9, 31.8 and 24.2 GPa, respectively. The computed transition pressures are consistent with the experimental results as well as previous theoretical calculations4,6,7.The calculated volumes as a function of pressure are in good agreement with the experimental data (see figure 1). The obtained volumes show a sharp discontinuity with volume collapse of 8.9 %, 7.6% and 7.0 % for CaS, CaSe and CaTe compounds respectively in B1 and B2 phases at the transition pressure which indicates a first order structural phase transitions in these three compounds as depicted in figure 1b, d & f. In addition, the obtained pressure-volume data is fitted to third order Birch-Murnaghan equation of state to calculate bulk modulus (and its pressure derivative), which are found to be 58.4 (4.3), 48.3 (4.2) and 37.6 (4.1) for CaS, CaSe and CaTe, respectively and are in good agreement with the experimental data4.
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S. C. Rakesh Roshan et al./ Materials Today: Proceedings 5 (2018) 18874–18878
(a)
(b)
(c)
(d)
(e)
(f)
Fig. 1 Calculated enthalpy and volume as a function of pressure for (a, b) CaS, (c, d) CaSe and (e, f) CaTe. Experimental data is taken from the ref4.
S. C. Rakesh Roshan et al./ Materials Today: Proceedings 5 (2018) 18874–18878
18877
2.2 Lattice dynamics of CaX compounds under high pressure At ambient conditions, CaX compounds crystallize in face centered cubic structure having space group Fm-3m with one formula unit i.e. two atoms per primitive cell resulting in 6 vibrational modes. Among the 6 vibrational modes (3N; N = no. of atoms), 3 are acoustic and remaining 3 (3N-3) are optical modes. The computed phonon spectra along high symmetry directions of the Brillouin zone at ambient as well as at high pressure. As shown in figure 2 (ac), the gap between acoustic and optical braches is increasing from CaS CaSe CaTe which is due to the mass difference between cation (Ca) and anion (S Se Te) and also this gap increases with increasing pressure. It is also found that CaS, CaSe and CaTe are dynamically stable since all the phonon frequencies are positive and no imaginary frequencies are found throughout the Brillouin zone. We also noticed that CaS, CaSe and CaTe compounds are dynamically stable even after the phase transition pressure till 50 GPa (which is the highest pressure of the present study) for both CaS and CaSe compounds whereas up to 30 GPa for CaTe in B1 phase which clearly represents the investigated compounds undergo structural transition of first order type.
(a)
(b)
(c) Fig. 2 Calculated phonon dispersion of (a) CaS, (b) CaSe at 0 and 50 GPa and (c) CaTe at 0 and 30 GPa.
3.Conclusions In conclusion, the structural and lattice dynamical properties of CaX (X = S, Se Te) compounds under high pressure up to 50 GPa were carried out using first principles calculations based on DFT. Pressure induced first order structural phase transitions from B1 to B2 were seen in CaS, CaSe and CaTe compounds at 34.9, 31.8 and 24.2 GPa with volume collapse of 8.9 %, 7.6 % and 7.0 %, respectively at the transition pressure. The obtained transitions
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S. C. Rakesh Roshan et al./ Materials Today: Proceedings 5 (2018) 18874–18878
pressures and magnitude of volume collapse are in good agreement with the experimental results. The calculated phonon spectra of CaX compounds in B1 phase are found to be dynamically stable even after the phase transition pressure to 50 GPa for CaS, CaSe whereas CaTe is stable up to 30 GPa of pressure. The separation of acoustic and optical phonon braches is increasing from CaS CaSe CaTe and also this gap increases with pressure. Acknowledgements Authors would like to acknowledge RGUKT Basar for providing the computational facilities. References [1] Y. Nakanishi, T. Ito, Y. Hatanaka, and G. Shimaoka, Preparation and luminescent properties of SrSe: Ce Thin-film, Appl. Surf. Sci. 66, 515–519 (1993). [2] R. Pandey and S. Sivaraman, Spectroscopic properties of defects in alkaline-earth sulfides, J. Phys. Chem. Solids, 52 211–225 (1991). [3] P. Cervantes, Q. Williams, M. Cote, M. Rohlfing, and M. L. Cohen, Band structures of CsCl-structured BaS and CaSe at high pressures implications for metallization pressure of the alkaline earth chalcogenides, Phys. Rev. B, 58 9793-9800 (1998). [4] H. Luo, R. G. Greene, K. G. Handehari, T. Li, A.L. Ruoff, Phys. Rev. B, 50, 16232 (1994). [5] P. Giannozzi, S. Baroni, N. Bonini, M. Calandra, R. Car, C. Cavazzoni, D. Ceresoli, G. L. Chiarotti, M. Cococcioni, I. Dabo, A. Dal Corso, S. Fabris, G. Fratesi, S. de Gironcoli, R. Gebauer, U. Gerstmann, C. Gougoussis, A. Kokalj, M. Lazzeri, L. Martin-Samos, N. Marzari, F. Mauri, R. Mazzarello, S. Paolini, A. Pasquarello, L. Paulatto, C. Sbraccia, S. Scandolo, G. Sclauzero, A. P. Seitsonen, A. Smogunov, P. Umari, R. M. Wentzcovitch, J. Phys. :Condens. Matter, 21, 395502 (2009). [6] K. Syassen, N.E. Christensen, H. Winzen, K. Fisher, J. Evers, Phys. Rev. B, 35, 4052 (1987). [7] K: S. Yamaoka, O. Shimomuro, H. Nakasawa, O. Fukunaga, Solid State Commun. 33, 87 (1980); J. Wang, S. Yip, Phys. Rev. Lett., 71, 4182 (1993).
ScienceDirect Materials Today: Proceedings 5 (2018) 18874–18878
www.materialstoday.com/proceedings
ICMPC_2018
Structure and Lattice Dynamics of Calcium Chalcogenides under High Pressure S. C. Rakesh Roshana, Lavanya Kunduruab, N. Yedukondalua*, and M. Sainatha a
Rajiv Gandhi University of Knowledge Technologies, RGUKT Basar, 504107, India b jntu hyderabad
Abstract We have investigated the structural and lattice dynamics of alkaline-earth chalcogenides namely CaX (X = S, Se Te) compounds under high pressure up to 50 GPa using plane wave pseudo potential approach based on density functional theory. It is found that CaS, CaSe and CaTe compounds undergo first order structural phase transitions from NaCl-type (B1) to CsCl-type (B2) phase at 34.9, 31.8 and 24.2 GPa respectively and the obtained transitions pressures are consistent with the experimental results. We have also calculated the phonon dispersions of these three compounds in B1 phase and are found to be dynamically stable even after the phase transition pressure to maximum pressure of the present study (50 GPa) for CaS, CaSe whereas CaTe is stable up to 30 GPa. © 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of Materials Processing and characterization. Keywords: Phonon dispersion;Density Fumctional Theory;
1. Introduction Calcium chalcogenide CaX (X = S, Se, and Te) compounds belong to the class of alkaline-earth chalcogenides. In one hand, they have been the subject of considerable interest from both theoretical and experimental perspective due to their technological applications in the fields of microelectronics, infrared-sensitive devices and luminescence1,2.
* Corresponding author. Tel.+91-9908797832 E-mail address: [email protected]
2214-7853 © 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of Materials Processing and characterization.
S. C. Rakesh Roshan et al./ Materials Today: Proceedings 5 (2018) 18874–18878
18875
On the other hand, high pressure research on structural phase transformations based on the theoretical calculations or measurements have become quite interesting in recent years, as they provide good insights in designing novel materials with specified properties at extreme conditions. Calcium chalcogenides possess rock-salt NaCl-type (B1) structure at ambient conditions and they transform to CsCl-type (B2) structure under application of hydrostatic pressure. These are closed shell ionic systems and have similar electronic structures and physical properties3. Structural studies of CaS, CaSe and CaTe under high pressure up to 52 GPa, have been carried out experimentally using x-ray diffraction technique and observe first order structural phase transitions from B1B2 phase4. The structural phase transitions are associated with many changes related to properties of the system from micro- to macroscopic level. Also, lattice dynamical calculations play a key role in determining the dynamical stability of materials at ambient as well as at high pressure. First principles calculations based on density functional theory (DFT) is a powerful tool to investigate pressure dependent structural and lattice dynamical properties of materials. In the present study, we have systematically investigated the pressure induced structural phase transitions and lattice dynamical properties of three calcium chalcogenides. 1.1. Computational details All the first principles calculations were carried out using plane wave pseudo potential approach implemented quantum espresso package5. Norm conserving pseudo potentials are used to treat the electron-ion interactions whereas electron-electron interactions are treated within generalized gradient approximation with Perdew-BurkeErnzerhof parameterization. The plane wave cutoff energy was set to 100 Ry and a k-mesh of 8×8×8 using Monkhorst-Pack grid scheme. Lattice dynamical properties were calculated using density functional perturbation theory (DFPT). Eight dynamical matrices were calculated using 4x4x4 q-mesh and are interpolated to compute the phonon spectra of the CaX compounds. 2. Results and Discussion 2.1 Structural phase transitions in CaX (S, Se, Te) compounds High pressure studies using first principles calculations provide deep insight for predicting novel phases of materials under high pressure for diverse applications. CaX compounds are simple binary systems to understand the structural phase transitions and their dynamical stability under high pressure. By considering the experimental data as input, we first optimized the lattice geometry of three investigated CaX compounds at ambient as well as at high pressure up to 50 GPa in both B1 and B2 phases. As illustrated in figure 1a, c & e, the calculated enthalpy as a function of pressure shows the CaS, CaSe and CaTe compounds undergo a structural phase transitions from B1 to B2 phase transitions at 34.9, 31.8 and 24.2 GPa, respectively. The computed transition pressures are consistent with the experimental results as well as previous theoretical calculations4,6,7.The calculated volumes as a function of pressure are in good agreement with the experimental data (see figure 1). The obtained volumes show a sharp discontinuity with volume collapse of 8.9 %, 7.6% and 7.0 % for CaS, CaSe and CaTe compounds respectively in B1 and B2 phases at the transition pressure which indicates a first order structural phase transitions in these three compounds as depicted in figure 1b, d & f. In addition, the obtained pressure-volume data is fitted to third order Birch-Murnaghan equation of state to calculate bulk modulus (and its pressure derivative), which are found to be 58.4 (4.3), 48.3 (4.2) and 37.6 (4.1) for CaS, CaSe and CaTe, respectively and are in good agreement with the experimental data4.
18876
S. C. Rakesh Roshan et al./ Materials Today: Proceedings 5 (2018) 18874–18878
(a)
(b)
(c)
(d)
(e)
(f)
Fig. 1 Calculated enthalpy and volume as a function of pressure for (a, b) CaS, (c, d) CaSe and (e, f) CaTe. Experimental data is taken from the ref4.
S. C. Rakesh Roshan et al./ Materials Today: Proceedings 5 (2018) 18874–18878
18877
2.2 Lattice dynamics of CaX compounds under high pressure At ambient conditions, CaX compounds crystallize in face centered cubic structure having space group Fm-3m with one formula unit i.e. two atoms per primitive cell resulting in 6 vibrational modes. Among the 6 vibrational modes (3N; N = no. of atoms), 3 are acoustic and remaining 3 (3N-3) are optical modes. The computed phonon spectra along high symmetry directions of the Brillouin zone at ambient as well as at high pressure. As shown in figure 2 (ac), the gap between acoustic and optical braches is increasing from CaS CaSe CaTe which is due to the mass difference between cation (Ca) and anion (S Se Te) and also this gap increases with increasing pressure. It is also found that CaS, CaSe and CaTe are dynamically stable since all the phonon frequencies are positive and no imaginary frequencies are found throughout the Brillouin zone. We also noticed that CaS, CaSe and CaTe compounds are dynamically stable even after the phase transition pressure till 50 GPa (which is the highest pressure of the present study) for both CaS and CaSe compounds whereas up to 30 GPa for CaTe in B1 phase which clearly represents the investigated compounds undergo structural transition of first order type.
(a)
(b)
(c) Fig. 2 Calculated phonon dispersion of (a) CaS, (b) CaSe at 0 and 50 GPa and (c) CaTe at 0 and 30 GPa.
3.Conclusions In conclusion, the structural and lattice dynamical properties of CaX (X = S, Se Te) compounds under high pressure up to 50 GPa were carried out using first principles calculations based on DFT. Pressure induced first order structural phase transitions from B1 to B2 were seen in CaS, CaSe and CaTe compounds at 34.9, 31.8 and 24.2 GPa with volume collapse of 8.9 %, 7.6 % and 7.0 %, respectively at the transition pressure. The obtained transitions
18878
S. C. Rakesh Roshan et al./ Materials Today: Proceedings 5 (2018) 18874–18878
pressures and magnitude of volume collapse are in good agreement with the experimental results. The calculated phonon spectra of CaX compounds in B1 phase are found to be dynamically stable even after the phase transition pressure to 50 GPa for CaS, CaSe whereas CaTe is stable up to 30 GPa of pressure. The separation of acoustic and optical phonon braches is increasing from CaS CaSe CaTe and also this gap increases with pressure. Acknowledgements Authors would like to acknowledge RGUKT Basar for providing the computational facilities. References [1] Y. Nakanishi, T. Ito, Y. Hatanaka, and G. Shimaoka, Preparation and luminescent properties of SrSe: Ce Thin-film, Appl. Surf. Sci. 66, 515–519 (1993). [2] R. Pandey and S. Sivaraman, Spectroscopic properties of defects in alkaline-earth sulfides, J. Phys. Chem. Solids, 52 211–225 (1991). [3] P. Cervantes, Q. Williams, M. Cote, M. Rohlfing, and M. L. Cohen, Band structures of CsCl-structured BaS and CaSe at high pressures implications for metallization pressure of the alkaline earth chalcogenides, Phys. Rev. B, 58 9793-9800 (1998). [4] H. Luo, R. G. Greene, K. G. Handehari, T. Li, A.L. Ruoff, Phys. Rev. B, 50, 16232 (1994). [5] P. Giannozzi, S. Baroni, N. Bonini, M. Calandra, R. Car, C. Cavazzoni, D. Ceresoli, G. L. Chiarotti, M. Cococcioni, I. Dabo, A. Dal Corso, S. Fabris, G. Fratesi, S. de Gironcoli, R. Gebauer, U. Gerstmann, C. Gougoussis, A. Kokalj, M. Lazzeri, L. Martin-Samos, N. Marzari, F. Mauri, R. Mazzarello, S. Paolini, A. Pasquarello, L. Paulatto, C. Sbraccia, S. Scandolo, G. Sclauzero, A. P. Seitsonen, A. Smogunov, P. Umari, R. M. Wentzcovitch, J. Phys. :Condens. Matter, 21, 395502 (2009). [6] K. Syassen, N.E. Christensen, H. Winzen, K. Fisher, J. Evers, Phys. Rev. B, 35, 4052 (1987). [7] K: S. Yamaoka, O. Shimomuro, H. Nakasawa, O. Fukunaga, Solid State Commun. 33, 87 (1980); J. Wang, S. Yip, Phys. Rev. Lett., 71, 4182 (1993).