Pressure-induced phase transition in ThO(2) and PuO(2)
Thorium and plutonium dioxides were studied under pressure by the energy dispersive X-ray diffraction method. A double conical slit assembly was used to collect simultaneously the diffracted radiation at five and seven degrees. ThO(2) undergoes a phase transformation at 40 GPa. The high-pressure phase remains stable up to 55 GPa (the highest pressure reached in the experiment). For PuO(2), a structural transformation occurs near 39 GPa. The observed high-pressure phases of ThO(2) and PuO(2) exhibit similar diffraction spectra. The ThO(2) and PuO(2) high-pressure phase has been indexed in the PbCl(2)-type structure. The bulk modulus has been calculated as B(0)=262 GPa with a pressure derivative of B'(0)=6.7 for ThO(2), and as B(0)=379 GPa with B'(0)=2.4 for PuO(2). The volume decrease at the transition is 12% for PuO(2) and 8% for ThO(2).
Bibliographic Reference: Article: High Pressure Research, Vol. 2 (1990) pp. 381-389
Record Number: 199110324 / Last updated on: 1994-12-02
Original language: en
Available languages: en