The Effect of Pressure on the Lattice Parameters Part I. PbS and PbTe Part II. Gd, NiO, and α-MnS

Abstract

The effect of pressure up to 90 kbar has been measured on the lattice parameters of PbS, PbTe, Gd, NiO, and α-MnS at room temperature. The X-ray powder patterns which correspond with SnS-type patterns were observed for PbS above 25 kbar and for PbTe above 45 kbar. The X-ray powder patterns which correspond with Sm-type patterns were observed for Gd above 28 kbar. The smoothed p – v data suggest the first-order transition from NaCl-type to SnS-type structures for PbS and PbTe and that from hcp-type to Sm-type structure for Gd, which are accompanied by the volume discontinuity of about 3, 2, and 1%, respectively. The pressure-induced transition in PbS and PbTe suggests by analogy to SnS-type compounds that the distortion in structure is associated with the anisotropic bonding function, which has been proposed by Gashimzade and Khartsiev. The effect of temperature has been calculated from the thermal data on the Grüneisen parameters of Gd, NiO, and α-MnS. The temperature dependence is explained by the contributions of the term of the lattice-vibrational Grüneisen parameters obtained from the p – v data and the term of the magnetic Grüneisen parameters obtained from the logarithmic dependence of ordering temperature with volume for the ferromagnetic and antiferromagnetic states.