Anisotropic compressibility and expansivity in layered GeSe2

Unit-cell dimensions of layered GeSe2 (P21/c, Z=16) are determined isothermally and isobarically by in situ high-temperature and high-pressure angle-dispersive X-ray diffraction. The isothermal bulk modulus KT, from a third-order Birch–Murnaghan equation of state with its first pressure derivative KT′=9.1±2.2, is 11.5±2.2 GPa (T=573 K, 0.0001 GPa≤P≤3.9 GPa). The isobaric volume expansivities αP are (9.03×10−5−7×10−9T)±0.3×10−5 K−1 and (8.39×10−5−7×10−9T)±0.3×10−5 K−1 at P=0.0001 GPa (298 K≤T≤773 K) and 1 GPa (298 K≤T≤614 K), respectively. Both the compressibility and the expansivity are largely anisotropic due to the two-dimensional structure of this compound.