Room temperature XRD patterns of HgGa2Se4 at selected pressures. In all diagrams, the background was subtracted. At 0.4 GPa, Bragg reflections are indicated with vertical ticks. Note that the (200) and (004) reflections are not seen because of their very low intensity which is less than 0.2% of the (112) peak intensity at 1 atm.
Lattice parameters of the DC phase of HgGa2Se4 as a function of pressure. Solid circles refer to experimental data. Ab initio results are plotted with solid (PBESol) and dashed (PBE) lines.
Volume of the DC phase of HgGa2Se4 as a function of pressure. Experimental data (solid circles) and their EOS fit (dash-dotted line). Theoretical results are plotted with solid (PBESol) and dashed (PBE) lines. The inset shows the evolution of the c/a ratio of the DC phase as a function of pressure. Dash-dotted line is a linear fit to the experimental c/a.
Left side of panel: κa and κc vs. pressure. Right side: (κa - κc) vs. pressure. Results correspond to: (a) XRD experiments, (b) PBE calculations, and (c) PBESol calculations.
Calculated cation-anion and vacancy-anion distances (a) and compressibilities (b) as a function of pressure for DC-HgGa2Se4. Solid (PBESol) and dashed (PBE) lines are used.
Pressure dependence of the theoretical (PBESol) elastic constants of DC-HgGa2Se4: (a) Seven Cij elastic constants and (b) Six C′ij elastic constants. Solid lines connecting the calculated data points are shown as a guide to the eyes.
Pressure dependence of (a) B, (b) G, (c) E, (d) ν, (e) B/G, and (f) A. Squares, circles, and triangles refer to the Voigt, Reuss, and Hill approximations. A factor data are shown for ϕκ = 0.76°. Solid lines connecting the calculated data points are shown as a guide to the eyes in panels (a) to (e). Solid line in panel (f) represents the behavior of A with pressure.
Experimental and theoretical crystallographic parameters of tetragonal (I-4, Z = 2) HgGa2Se4 at room conditions. Hg, Ga(1), and Ga(2) are located at the 2 a (0,0,0), 2 b (0,0,0.5), and 2 c (0,0.5,0.25) Wyckoff positions, respectively. The vacancy is located at the 2 d (0,0.5,0.75) Wyckoff position. The relative atomic coordinates of the Se anion located at the 8 g (x,y,z) Wyckoff position are given in the table.
Experimental and theoretical (Th.) volume (V0), bulk modulus (B0), and its pressure derivative (B0′) here obtained for DC-HgGa2Se4 at zero pressure using a third-order BM EOS.
Distance compressibility κ (in 10 − 3 GPa−1) obtained from our calculations at zero pressure. For DC-HgGa2Se4, data of the Hg-Se, average Ga-Se, and vacancy-Se distances are shown. For HgSe, data of the Hg-Se distance are shown. For ε-GaSe, data of Ga-Se and Se(1)-Se(2) distances are shown. Theoretical (th.) and experimental (exp.) values for B0 (in GPa) at zero pressure are also included.
Seven C ij elastic constants (in GPa) for DC-HgGa2Se4. The set of six C′ij (C′ 16 = 0) elastic constants are also given. The elastic moduli B, G, and E (in GPa) and Possion's ratio (ν) are given in the Voigt, Reuss, and Hill approximations, labeled, respectively, with subscripts V, R, and H. The B/G ratio and the shear anisotropy factor (A) are also given. The values for κa and κc have been obtained from the Sij elastic compliances tensor by using Eqs. (10) . All given data has been calculated with the PBESol prescription at zero pressure. Calculated data for DC-CdGa2Se4 and DC-CdGa2S4 are also added. 63
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