The electronic structure of elemental silicon has been studied under high pressure using high-energy Compton scattering utilizing synchrotron radiation. The experiment was realized using a special Laue monochromator and a novel assembly of compound refractive lenses. The extremely good focusing enabled us to utilize a Mao-Bell version of the Merrill-Basset diamond anvil cell with a Be gasket up to a pressure of 20 GPa. After the careful subtraction of background scattering, the Compton profile difference for the metastable Si-XII to the Si-V phase was extracted and compared with the theory. The results clearly demonstrate the feasibility and potential of the Compton scattering technique as a complementary tool in the study of electronic structure of materials under high pressure.
Pressure-induced structural changes could induce changes in transport properties and lead to a better understanding of the structure−property relationship. The evolution of the carrier transport properties of BiFeO 3 (BFO) ceramics under a high pressure was investigated through impedance spectroscopy measurements at room temperature combined with first-principles calculations. A pressure-induced abnormal transition from pure electronic to mixed ionic−electronic was found in the BFO ceramics Cmmm and Pnma phases at 7.67 and 11.01 GPa, respectively. The pressure-induced structural phase transition from the R3c phase to Cmmm and then to Pnma was responsible for the change in electrical transport behavior from pure electronic to mixed ionic− electronic conduction, accompanied by a decrease in ionic resistance. The calculations of electronic structures and electron localization function from 1 atm to 40 GPa indicated that the ionic conduction in the Pnma phase resulted from the weakened Coulomb screen of the localized electron background to O 2− between Bi 3+ and O 2− . This work provides a critical insight into the understanding of the relationship between structure and conduction and facilitates the application of ferroelectric materials in photoelectric fields.
The significant conductivity enhancement of semiconductor BiOI up to 19.2 GPa has provided an example of the directed regulation of the electrical properties of BiOX layered materials using controllable pressure.
Investigating the thermal transport properties of materials is of great importance in the field of earth science and for the development of materials under extremely high temperatures and pressures. However, it is an enormous challenge to characterize the thermal and physical properties of materials using the diamond anvil cell (DAC) platform. In the present study, a steady-state method is used with a DAC and a combination of thermocouple temperature measurement and numerical analysis is performed to calculate the thermal conductivity of the material. To this end, temperature distributions in the DAC under high pressure are analyzed. We propose a three-dimensional radiative–conductive coupled heat transfer model to simulate the temperature field in the main components of the DAC and calculate in situ thermal conductivity under high-temperature and high-pressure conditions. The proposed model is based on the finite volume method. The obtained results show that heat radiation has a great impact on the temperature field of the DAC, so that ignoring the radiation effect leads to large errors in calculating the heat transport properties of materials. Furthermore, the feasibility of studying the thermal conductivity of different materials is discussed through a numerical model combined with locally measured temperature in the DAC. This article is expected to become a reference for accurate measurement of in situ thermal conductivity in DACs at high-temperature and high-pressure conditions.
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