Anisotropic compressibility and expansivity in layered GeSe2

Unit-cell dimensions of layered GeSe2 (P2(1)/c, Z = 16) are determined isot hermally and isobarically by in situ high-temperature and high-pressure ang le-dispersive X-ray diffraction. The isothermal bulk modulus K-T, from a th ird-order Birch-Murnaghan equation of state with its first pressure derivat ive K-T' = 9.1 +/- 2.2, is 11.5 +/- 2.2 GPa (T = 573 K, 0.0001 GPa less tha n or equal to P less than or equal to 3.9 GPa). The isobaric volume expansi vities ap are (9.03 x 10(-5) - 7 x 10(-9)T) +/- 0.3 x 10(-5) K-1 and (8.39 x 10(-5) - 7 x 10(-9)T) +/- 0.3 x 10(-5) K-1 at P = 0.0001 GPa (298 K less than or equal to T less than or equal to 773 K) and 1GPa (298 K less than o r equal to T less than or equal to 614 K), respectively. Both the compressi bility and the expansivity are largely anisotropic due to the two-dimension al structure of this compound. (C) 2000 Elsevier Science Ltd. All rights re served.