The pressure-volume relation of ytterbium has been determined up to 9 Gpa using tungsten carbide opposed anvil high pressure x-ray camera. The fcc phase of ytterbium is observed between one atmosphere and 4 GPa and the bcc phase above 3·5 GPa. The bcc phase can be metastably retained down to 1 GPa by gradually decreasing the pressure from a region where only bcc phase alone is observed. The bulk modulus,B0, at zero pressure and the pressure derivative of the bulk modulus,B’0, are determined by fitting Murnaghan equation to the pressure-volume data. The following values were obtained:B0=16·3 GPa andB’0=3·6 for the fcc phase, andB0=14·7 GPa andB’0=1·5 for the bcc phase. Based on the present data it is suggested that the thermodynamic equilibrium pressure for fcc ⇆ bcc transformation in ytterbium is below 3·5 GPa. The valence change under pressure has been discussed.
Volume 43, 2020
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