Structural phase transition in GaMo4Se8 and AlMo4S8 by X-ray powder diffraction

François, Μ.; Alexandroν, Ο. V.; Yvon, K.; Yaich-Aerrache, H. Ben; Gougeon, P.; Potel, M.; Sergent, M.

doi:10.1524/zkri.1992.200.14.47

Cited by 5 publications

(7 citation statements)

References 7 publications

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“…At T = 50 K, the (111) cubic peak splits into 3 peaks, with the two outer peaks corresponding to an R3m distortion. Previous X-ray diffraction studies of the structural phase transition of GaMo 4 Se 8 have rationalized the presence of extra peaks below the transition temperature (T = 51 K) as the coexistence of the high temperature cubic F 43m phase and the rhombohedral R3m phase [10]. However, with high-resolution measurements employed here, we find that the low-temperature data cannot be fit by a combination of the R3m phase and the F 43m phase.…”

Section: Resultscontrasting

confidence: 63%

“…At low temperatures, these materials crystallize in the polar R3m space group [9] and support complex magnetic phase diagrams with an ordered moment of 1 µ B /V 4 cluster. The related Mocontaining compounds, GaMo 4 S 8 and GaMo 4 Se 8 , have been less studied, although they are reported to have a similar low temperature crystal structure, but with a compressive rather than elongative distortion along the cubic [111] direction [9][10][11].…”

Section: Introductionmentioning

confidence: 99%

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Structural evolution and skyrmionic phase diagram of the lacunar spinel GaMo$_4$Se$_8$

Schueller,

Kitchaev,

Zuo

et al. 2020

Preprint

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Section: Resultscontrasting

confidence: 63%

Section: Introductionmentioning

confidence: 99%

Structural evolution and skyrmionic phase diagram of the lacunar spinel GaMo$_4$Se$_8$

Schueller,

Kitchaev,

Zuo

et al. 2020

Preprint

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“…GaV 4 S 8 , GaV 4 S 8 , GaMo 4 S 8 , and GaMo 4 Se 8 , however, undergo symmetry-lowering structural Jahn-Teller (JT) transitions at ≈40 K from F 43m to R3m (space group no. 160), [6][7][8] followed by spontaneous magnetic ordering at a lower Curie temperature T C [Figure 1(d)]. These displacive distortions lead to a unit cell of slightly different volume, lattice parameters, and rhombohedral angle α rh .…”

Section: A Crystal Structure Electrical and Magnetic Propertiesmentioning

confidence: 99%

“…5 After decades of continuous studies on various properties of the lacunar spinel compounds, the mechanism of these phase transitions as well as the proper theoretical approaches to describe various electronic states are still unclear. For instance, while the vanadium and molybdenum compounds can undergo symmetry-lowering structural phase transitions at low temperature, [6][7][8] the niobium and tantalum lacunar spinels remain in the highsymmetry cubic phase over a broad temperature range. 9 One of the possible reasons for this behavior in the family may be attributed to variations in the strength of electron-electron interactions, 6 since electron-correlation effects are expected to be stronger in 3d rather than 5d transition metals.…”

Section: Introductionmentioning

confidence: 99%

Assessing exchange-correlation functional performance in the chalcogenide lacunar spinels GaM4Q8 (M=Mo,

2019

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We perform systematic density functional theory (DFT) calculations to assess the performance of various exchange-correlation potentials Vxc in describing the chalcogenide GaM4Q8 lacunar spinels (M=Mo, V, Nb, Ta; Q=S, Se). We examine the dependency of crystal structure (in cubic and rhombohedral symmetries), electronic structure, magnetism, optical conductivity, and lattice dynamics in lacunar spinels at four different levels of Vxc: the local density approximation (LDA), generalized gradient approximation (GGA), meta-GGA, and hybrid with fractional Fock exchange. We find that LDA significantly underperforms GGA and higher level functionals in predicting lattice constants. LDA also fails to properly describe the magnetism in the family, and for some compositions it does not find the ground state distorted crystal structure. The Perdew-Burke-Ernzerhof (PBE) and PBE revised for solids (PBEsol) GGA functionals perform reasonably well in predicting lattice constants as well as the electronic structures. We find that the GGA with an on-site Coulomb interaction (GGA+U ) is unnecessary to produce a semiconducting state in the distorted polar R3m phase. Plus Hubbard U values ranging from 1∼2 eV, however, improve the quantitative performance of the GGA functionals. The meta-GGA functional SCAN predicts reasonable lattice constants and electronic structures; it exhibits behavior similar to the GGA+U functionals for small U values. The hybrid functional HSE06 is accurate in predicting the lattice constants, but leads to a band gap of ≈1 eV in the rhombohedral phase, which is higher than the experimental estimation of 0.2 eV. All of the lacunar spinels in the cubic phase are metallic at these levels of band theory, however, the predicted valence bandwidths are extremely narrow (≈0.5 eV). The cubic vanadium chalcogenides are found to be highly spin-polarized, which contrasts previous experimental results. We also find that these Vxc potentials do not quantitatively agree with the available experimental optical conductivity on GaV4S8; nonetheless, the LDA and GGA functionals correctly reproduce its lattice dynamical modes. Our findings suggest that accurate qualitative and quantitative simulations of the lacunar spinel family with DFT requires careful attention to the nuances of the exchange-correlation functional and considered spin structures. arXiv:1905.09170v1 [cond-mat.mtrl-sci]

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“…In GaMo 4 S 8 , GaMo 4 Se 8 , AlMo 4 S 8 , GaV 4 S 8 , and GaV 4 Se 8 , a Jahn–Teller-type structural phase transition has been observed at low temperature ( T JT ) resulting in a distorted cell with a polar rhombohedral symmetry of space group R 3 m . In the Mo compounds, this distortion compresses the noncentrosymmetric cubic lattice along one of its four [111] axes, reducing the point symmetry of the B 4 tetrahedra from T d to C 3 v .…”

Section: Introductionmentioning

confidence: 99%

Mode Crystallography Analysis through the Structural Phase Transition and Magnetic Critical Behavior of the Lacunar Spinel GaMo₄Se₈

et al. 2021

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In the lacunar spinels, with the formula AB 4 X 8 , transition-metal ions form tightly bound B 4 clusters resulting in exotic physical properties such as the stabilization of Néel-type skyrmion lattices, which hold great promise for energy-efficient switching devices. These properties are governed by the symmetry of these compounds with distortion of the parent noncentrosymmetric F 4̅3 m space group to the polar R 3 m , with recent observation of a coexisting Imm 2 low-temperature phase. In this study, through powder neutron diffraction, we further confirm that a metastable Imm 2 coexists with the R 3 m phase in GaMo 4 Se 8 and we present its structure. By applying the mode crystallography approach to the distortions together with anisotropic microstrain broadening analysis, we postulate that the formation origin of the minority Imm 2 phase stems from the high compressive stress observed in the R 3 m phase. Bond valence sum analysis also suggests a change in electronic configuration in the transition to Imm 2 which could have implications on the electrical properties of the compound. We further establish the nature of the magnetic phase transition using critical exponent analysis obtained from single-crystal magnetization measurements which shows a mixture of tricritical mean-field and 3D Heisenberg behavior [β = 0.22(4), γ = 1.19(1), and δ = 6.42(1)]. Magnetoentropic mapping performed on a single crystal reveals the signature of a positive entropy region near the magnetic phase transition which corresponds to the skyrmion phase field observed in a polycrystalline sample.

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Structural phase transition in GaMo₄Se₈ and AlMo₄S₈ by X-ray powder diffraction

Abstract: GaMo 4 Se 8 (I) and A1MO 4 S 8 (Π) transform at T x = 45(2) Κ and 24(2) K, respectively, from a cubic high-temperature modification with ordered defect spinel structure (space group F43m, a = 10.

Cited by 5 publications

References 7 publications

Structural evolution and skyrmionic phase diagram of the lacunar spinel GaMo$_4$Se$_8$

Structural evolution and skyrmionic phase diagram of the lacunar spinel GaMo$_4$Se$_8$

Assessing exchange-correlation functional performance in the chalcogenide lacunar spinels GaM4Q8 (M=Mo,

Mode Crystallography Analysis through the Structural Phase Transition and Magnetic Critical Behavior of the Lacunar Spinel GaMo₄Se₈

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Structural phase transition in GaMo4Se8 and AlMo4S8 by X-ray powder diffraction

Abstract: GaMo 4 Se 8 (I) and A1MO 4 S 8 (Π) transform at T x = 45(2) Κ and 24(2) K, respectively, from a cubic high-temperature modification with ordered defect spinel structure (space group F43m, a = 10.

Cited by 5 publications

References 7 publications

Structural evolution and skyrmionic phase diagram of the lacunar spinel GaMo$_4$Se$_8$

Structural evolution and skyrmionic phase diagram of the lacunar spinel GaMo$_4$Se$_8$

Assessing exchange-correlation functional performance in the chalcogenide lacunar spinels GaM4Q8 (M=Mo,

Mode Crystallography Analysis through the Structural Phase Transition and Magnetic Critical Behavior of the Lacunar Spinel GaMo4Se8

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Structural phase transition in GaMo₄Se₈ and AlMo₄S₈ by X-ray powder diffraction

Mode Crystallography Analysis through the Structural Phase Transition and Magnetic Critical Behavior of the Lacunar Spinel GaMo₄Se₈