Phase Relations and Pressure-Volume-Temperature Equation of State of Galena

The phase relations and pressure volume dependences of galena (PbS) under high pressure and high temperature are investigated by means of in situ observation using resistance heating in a diamond anvil cell and synchrotron radiation. The phase transition from NaCl type to TlI type takes place at approximately 2.4 GPa. A fit to the high temperature third-order Birch-Murnaghan equation of state yields an isothermal bulk modulus K₀ = 37(3) GPa, and its pressure derivative K'₀ =3.6(3), the temperature derivative of the bulk modulus (∂K/∂T)_P=-0.022(9) GPaK^-1, and the thermal expansion coefficient α₀ =2.2(5)× 10^-5 K^-1 for TlI-type galena. The linear compressibilities β along a, b and c directions of TlI type is elastically anisotropic (β_a =3.4× 10^-3 GPa^-1, β_b =1.4×10^-4 GPa^-1 and β_c =1.6× 10^-3 GPa^-1). We obtain the temperature derivative of the bulk modulus (∂K/∂T)_P and thermal expansion coefficient α₀ for TlI-type galena for the first time.