| The use of traditional four-electrode method in the diamond anvil cell (DAC) on the samples in situ conductivity measurement,in the experiment the gasket is the metal gasket. because the metal has a good plastic flow, it also has a certain hardness and strength. Therefore, made of metal gasket can provide a good balanced seal pressure environment.the DAC high-pressure experiments often use the metal as the gasket, it can provide effective sealing pressure environment. However, there is a high electrical conductivity of metal, usually aluminum oxide thin film deposition method to achieve electrode and metal insulation, wall insulation but are often ignored. Often are not insulated wall, so that measurements can lead to a current through the inside metal gasket, or even electric, the result is the sample resistivity measurement results of a huge error.When the sample conducts, the metal wall of cavity pressure measurement circuit of the bypass will cause effects. There would be current through the gasket, the higher the conductivity of the sample, the more obvious effects of bypass. Therefore, the purpose of this study is to take some of the ways in which the metal gasket wall insulation, reduce or even eliminate bypass effect, make the experiment more realistic and accurate.In this paper, ANSYS software simulats the gasket within the sample chamber of the current distribution of the sample in the steady current field simulation, found that when the wall insulation and wall models are not insulated by the model has very different . When the wall is not insulated, the electric potential distribution within the sample chamber and the gasket, indicating a current through the gasket, it will cause the sample chamber of the sample resistivity is not accurate. When the wall insulation when there is no current through the metal gasket, so that will not short-circuit electrodes, measuring the sample resistivity will be very accurate.In the simulation, based on this paper, PMMA as insulating materials of metal pressure cavity wall insulation. The use of traditional four-electrode method in the diamond anvil cell (DAC) in situ conductivity measurements of samples, usually using the four-electrode method. But the four-probe method in the measurement process pressure in the gasket hole can not fill out additional samples, only fill in the sample chamber , which increases the difficulty of filling and measurement accuracy. The other four electrode measurements without the need for PMMA and acetone, the mixture of sample data and use this mixture compared the measured data, measurement of wall is insulated so the instability of factors, only moderate viscosity, the wall is hard. As the gasket hole the size of the spacer thickness, the number of samples of Tim installed, the pressure is not balanced presence of destabilizing factors such as each measurement is somewhat different, as when atmospheric pressure to 30GPA PMMA sidewall insulation in the recent, insulation deterioration.Using the concentration of 17% PMMA solution as a insulating layer after curing, then there is no wall insulation and DAC to measure the resistivity of the samples, comparing the two methods can be seen fully insulated metal wall and metal gasket wall insulation finish is very different, the measured resistivity values quite different, with the wall fully insulated pads measured resistivity values than the side wall is not insulated by a large multi-measurements, shows the sample conductive wall insulation must be taken into account .This work will improve the measurement accuracy of the conductivity under high pressure is very important technical aspects, not only overcome the effects of lateral bypass will also improve the uniformity of pressure within the DAC.
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