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Abstract
We report an original technique for the precise measurement of a plunger's displacement of a high-pressure cell under loading up to 30 GPa. We show that the method gives information about changes in mechanical properties of a microsample, such as volume shrinkage and compressibility. The technique was examined on several materials, such as CaCO3, ZnO, GaAs, and CeNi. For calcium carbonate (CaCO3), the volumetric changes were seen near 2 GPa, which corresponds to the calcite→aragonite transition. Likewise, the volumetric changes in zinc oxide (ZnO) appeared near 8.5–10 GPa, in consistence with the wurtzite→rock salt transformation. In gallium arsenide (GaAs), two transitions under pressure were found near 14–15 and 19 GPa, in agreement with the recent observations of intermediate phases (e.g. cinnabar) between the ambient zinc blende and the metallic Cmcm one. In CeNi alloy, two features were noticed: first a significant volumetric reduction near 5 GPa and then a slight bend in a contraction curve near 10–12 GPa. These were proposed to be related to structural transformations which were also found in thermoelectric power (Seebeck effect) and X-ray diffraction studies. The developed technique of measurement of a sample's contraction may be supplementary to transport measurements in an anvil cell.
Acknowledgements
The authors are grateful to Dr E. Lavrov (Dresden TU) for kindly providing single crystals of ZnO. Polycrystalline samples of CeNi were synthesized by Dr S.N. Naumov (IMP) and were characterized using neutron diffraction by Dr V.I. Voronin (IMP). The work was partly supported by the RFBR, #07-08-00338 and the Program of Presidium of RAS, grant #18.