A.M. Redon

Electronic and crystallographic transitions induced by pressure in CeP

The isomorphous transformation of CeP previously reported near 10 GPa is confirmed but the relative volume decrease Delta V/V0 is reduced from 7.5% to 3% because of a smaller bulk modulus at lower pressures. This difference is attributed to large anisotropic stress components which were not taken into account in previous experiments. The cubic NaCl-type phase is stable up to 19 GPa at which a crystallographic change to the cubic CsCl-type structure occurs with a volume decrease of 10.5%. The results are discussed in terms of the valence change and the Kondo concentrated-system models.

Pressure-volume relationships for CeSe and CeBe13 up to 25 GPa

Abstract The variations in the volumes of CeSe and CeBe13 have been determined by powder X-ray diffraction in a diamond anvil cell up to 25 GPa at room temperature. In each case, the bulk modulus and its first pressure derivative have been determined. They do not indicate the presence of any negative contribution due to a Kondo volume-dependent interaction or a pressureinduced valence change. A crystallographic phase transformation to a cubic CsCl-type structure has been evidenced for CeSe above 18 GPa.

Absence of discontinuity in the pressure-volume dependence of CeAl2 and CeIn3

X-ray diffraction experiments performed on the Kondo compounds CeAl2 and CeIn3, under both hydrostatic and quasi-hydrostatic conditions, show a continuous behaviour, contrary to previous results on CeAl2. An anomalously low pressure derivative of the bulk modulus is however observed in both systems, leading to a unit-cell volume at 20 GPa about 4.5% smaller than what is expected for a normal trivalent material. These results are compared with those for pure cerium metal and possible interpretations in terms of valence change and compressible Kondo models are discussed.

Pressure-volume behaviour of UP, USb and UTe

Abstract The pressure-volume dependences of UP, USb and UTe have been determined by X-ray powder diffraction in a diamond anvil cell. To obtain reliable variations it is essential to account for the effects of anisotropic stress components. UP maintains its cubic NaCl-type structure at least up to 25 GPa while USb undergoes a cubic NaClCsCl type transformation at 8 GPa. The experimental data have been fitted to a Birch equation of state and the bulk moduli so obtained are compared to theoretical values. The presence of a Kondo effect in UTe is assumed to be responsible for its low bulk modulus.

High pressure X-ray studies of UAs and UTe

Abstract The volumes of UAs and UTe have been determined as a function of pressure by X-ray powder diffraction in a diamond anvil cell up to 25 GPa at room temperature. Both compounds exhibit a transition from the cubic NaCl-type to CsCl-type structure under high pressure. The bulk modulus and its first pressure derivative have been determined for each phase. In uranium monopnictides the variation of the bulk modulus as the − 5 3 power of the unit cell volume and the large bulk modulus of UAs compared to NpAs give support to 5f delocalization. The bulk modulus of UTe has an exceptionally low value and the possibility of a mixed valence state as in TmSe is discussed.

Electronic transitions induced by pressure in cerium monochalcogenides and monopnictides

Abstract The pressure volume variations of CeX compounds (X  O, Te, Sb, Bi) have been measured by X-ray diffraction on powdered samples in a diamond anvil cell up to 25 GPa. The bulk moduli and the first pressure derivatives have been calculated for all phases. From their values, the occurence of a continuous electronic transition is inferred in the NaCl-type phase of CeTe and CeBi; it is then followed by a back electronic discontinuous transition at the crystallographic transformation. In CeSb no electronic transition has been detected; the case of CeO is discussed.

High-pressure diffraction study of CeAl2 up to GPa

Abstract The compression curve of CeAl2 has been measured by X-ray diffraction up to 20 GPa. The results do not confirm the discontinuous valence transition that had been reported to occur near 6.5 GPa. Comparison with the normal trivalent compound LaAl2 reveals an anomalous softening of the CeAl2 lattice extending over the entire pressure range.

High pressure v-ray study of UP and USb☆

Abstract The pressure-volume dependences of UP and USb have been determined up to 25 GPa by v-ray powder diffraction in a diamond anvil cell. At normal pressure their bulk moduli are evual to 102 and 72.7 GPa respectively. UP maintains its NaCl-type structure while at 8 GPa USb undergoes a crystallographic phase transformation to the CsCl-type structure. At normal pressure the bulk moduli of the uranium monopnictides follow the Anderson-Nafe relation.