High-pressure behavior and thermoelastic properties of niobium studied by in situ x-ray diffraction

摘要: In situ synchrotron energy dispersive x-ray diffraction (XRD) experiments on Nb have been conducted at pressures up to 6.4 GPa and temperatures 1073 K. From the pressure-volume-temperature measurements, thermoelastic parameters were derived for first time based thermal pressure (ΔPth) equation of state (EOS), modified high-T Birch-Murnaghan EOS, Mie-Gruneisen-Debye EOS. With derivative bulk modulus KT′ fixed 4.0, we obtained ambient isothermal KT0 = 174(5) GPa, temperature constant (∂KT/∂T)P=−0.060(8) GPa K−1 volume (∂KT/∂T)V=−0.046(8) GPa K−1, volumetric expansivity αT(T)=2.3(3)×10−5+0.3(2)×10−8T (K−1), as well dependence expansion (∂α/∂P)T=(−2.0±0.4)×10−6 K−1 GPa−1. Fitting present data EOS with Debye Θ0 = 276.6 K gives γ0 = 1.27(8) KT0 = 171(3) a value q = 3.0. The isot...