| The advent of high pressure technique allows the rich insight into the physical and chemical properties of materials at high pressure conditions. Especially the generation of diamond anvil cell (DAC) made high pressure research a wide prospect, such as high pressure X-ray diffraction, high pressure Raman spectroscopy, high pressure phase transition, and high pressure electrical measurement et al.. While the laser heating technique was created, combined with high pressure device, some properties can be conducted at extreme pressure-temperature conditions. Electrical conductivity measurement has been a challenging problem for the complexity of aligning the conducting wires in the complicated loading procedure in the sample chamber. It is very difficult to take advantage of the laser heating technique in resistivity measurement under high P-T. In this paper, using depositing technique, we successfully solve this problem. By this device, we measured the electrical properties of solid and molten olivine, as well as FeS. Moreover, the equation of state of diaspore was investigated at high P-T.In the study of solid olivine, it is found that the conductivity increases with increasing temperature but decreases with increasing pressure, and our experimental results are consistent with previous resistance measurements at lower temperatures. The activation energy is 0.926 ev and 0.952 ev when pressure is 31 GPa and 35 GPa, and the activation volume is 0.236 cm3mol-1. The value of activation energy increases with the increasing pressure, but the effect is feeble. We could find a general tendency ofΔV from the results of Xu et al and the present experiment even though the staring sample is different. The activation volume of our sample is much smaller than that of Xu et al in Mg1.8Fe0.2SiO4 sample at 4-10GPa, indicating less the lattice deformation in the present sample. The reason is that the different ratio of Fe/Mg, also maybe relating the different phase (In our experiment the silicate isγphase with perovskite structure mixed with oxide, and it isαphase in the experiment of Xu et al).In the study of molten olivine, according to the previous explanation, the electrical conductivity of molten state is almost independent of oxygen fugacity under high pressure, so here we also do not take account into the oxygen fugacity. As observed in our experiment, the electrical conductivity increases noticeably with rising temperature. Different from temperature effect, the conductivity decreases slightly with increasing pressure, which is consistent with the results given by some previous reports and inconsistent with those reported by Watanabe et al.. The activation enthalpy obtained form our experiment is 0.785 eV at 10.6 GPa and 0.806 eV at 13.2 GPa. Compared to the results of solid olivine, the activation enthalpy of the molten sample is noticeably smaller. This difference is considered to be caused by the weakening and disordering of the phonon scattering in molten state. Yet we cannot rule out whether the discrepancies of the Fe/Mg ratio of the samples bring the difference. We also noticed that the effect of temperature on the conductivity of the molten sample is much smaller than that of the solid sample. Although the temperature range in our experiments does not cover that at the high conductivity zones, our results seem to support Karato's result that the high conductivity found in this region is then not introduced by olivine melting.In the study of FeS, the result represented that the conductivity of FeS existed as NiAs structural phase was smaller than that of the other phases by several magnitudes. The phase transitions ofsemiconductor-semimetal-metal were approved. During compression, four abnormal changes were found, in which two occurred at 4.7 GPa and 62.3 GPa have not been reported previously.In the study of diaspore, using synchrotron X-ray diffraction, the paper described the behavior of diaspore under HPHT. The bulk modulus was obtained by DFT based plane-wave pseudo-potential approach. A conclusion was made that the difference of compressibility for three axes changed small gradually with the increasing of pressure.In summary, the introduction of alumina layer improves the heating quality in electrical measurement at high P-T. This design exhibits a very good prospect for conductivity measurement in extreme P-T conditions. Thus far, most high temperature experiments about conductivity measurement were conducted in large cavity press. Due to the very small cavity and the high temperature oxidation of diamond, it is impossible to use high temperature technique and DAC technique simultaneously. Here we solved this problem in experiment.We conquer a series of difficulties of heat lost, microcircuit integration and thickness measurement in DAC experiments. Our technique extended the ranges of pressure and temperature, and it should be an innovation of technique and approach for studying the transport properties of matters at extreme conditions.
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