The transition metal dichalcogenide (TMD) ReS is a promising material for optoelectronic devices because of its remarkable quantum yield. Pressure can effectively tune the optoelectronic properties of TMDs through control of the atomic displacement. Here, we systematically investigated the lattice and electronic structural evolutions of compressed multilayer ReS. Both Raman spectra and first-principles calculations suggest the occurrence of an intralayer phase transition followed by an interlayer transition. A transition from one indirect to another indirect bandgap at 2.7 GPa was revealed by both high-pressure photoluminescence (PL) measurements and first-principles calculations, this behavior was elucidated by considering the fundamental relationship between lattice variation and electronic evolution. Moreover, by comparing the high-pressure behavior of MoS and ReS, we demonstrated interlayer coupling plays a critical role in determining the lattice and electronic structures in compressed TMDs. Our findings suggest the potential application of ReS in fabricating various stacking devices with tailored properties.

The electrical transport and structural properties of tin oxide nanoparticles under compression have been studied by in situ impedance measurements and synchrotron X-ray diffraction (XRD) up to 27.9 GPa. It was found that the conduction of SnO2 can be improved significantly with compression. Abnormal variations in resistivity, relaxation frequency, and relative permittivity were observed at approximately 12.3 and 25.0 GPa, which can be attributed to pressure-induced tetragonal- orthorhombic-cubic structural transitions. The dielectric properties of the SnO2 nanoparticles were found to be a function of pressure, and the dielectric response was dependent on frequency and pressure. The dielectric constant and loss tangent decreased with increasing frequency. Relaxation-type dielectric behaviour dominated at low frequencies. Whereas, modulus spectra indicated that charge carrier short-range motion dominated at high frequencies.

The study on the thermal transport properties of matter under high pressure is important but is hard to fulfill in a diamond anvil cell (DAC) because the accurate measurement of the temperature gradient within the sample of DAC is very difficult. In most cases, the sample temperature can be read accurately from the thermocouples that are directly attached to the lateral edges of diamond anvils because both the sample and diamond anvils can be uniformly heated up to a given temperature. But for the thermal transport property studies in DAC, an artificial temperature distribution along the compression axis is a prerequisite. Obviously, the temperature of the top or bottom surface of the sample cannot be substituted by that of diamond anvils although diamond anvils can be considered as a good medium for heat conduction. With temperature field simulation by finite element analysis, it is found that big measurement errors can occur and are fatal to the correct analysis of thermal transport properties of materials. Thus, a method of combining both the four-thermocouple configuration and temperature field analysis is presented for the accurate temperature distribution measurement in DAC, which is based on the single-function relationship between temperature distribution and sample thermal conductivity.

In situ impedance measurements were employed to investigate the electrical transport properties of BaMoO under pressures of up to 20.0 GPa. Two anomalous changes in the electrical parameters were found, related to the pressure-induced structural phase transitions. The dielectric performance of BaMoO was improved by pressure. The dispersion in the real part of dielectric constant versus frequency weakens with increasing pressure. Based on the first-principles calculations, the increases of resistance with increasing pressure in the tetragonal and monoclinic phases were mainly caused by the increasing defect levels. The decrease of the relative permittivity in the tetragonal phase was attributed to pressure-induced strengthening in electronic localization around Mo atoms, which hindered the polarization of Mo-O electric dipoles.

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In situ impedance measurement and first-principles calculations have been performed to investigate the effect of high pressure (up to 35.5 GPa) on the dielectric properties of SrMoO4. It is found that the carrier transport process is dominated by the grains, and the variation in resistance under compression is related to the change in activation energy. The relative permittivity of the tetragonal phase of SrMoO4 is stable below 7.0 GPa and has stable electrical storage capacity as well. However, the electron localization around O atoms in the monoclinic phase is enhanced with the increase in pressure, resulting in a decreased relative permittivity. A typical dielectric loss by electronic conduction of SrMoO4 is also presented. After unloading pressure, the dielectric loss of the low-frequency region is significantly reduced. Besides, the dielectric performance of SrMoO4 is effectively optimized by pressure. This study will provide a theoretical and experimental basis for the design and modification of other related ABO4-type materials for dielectric devices.

The influence of grain sizes, size effects, has long been a key factor influencing the properties and even the phase transformation pathways of nanomaterials and has resulted in a lot of intriguing abnormal phenomena. The mechanism behind these peculiar phenomena of nanomaterials remains unresolved. In this study, we performed high-pressure electrical and spectroscopic measurements on nanoanatase TiO 2 with average grain sizes of 11 and 62 nm, respectively, to characterize the relation between size effects and its electrical properties and thus reveal the mechanism behind these phenomena. Our work has demonstrated that the size effects on TiO 2 with certain grain sizes exhibit considerable influence on tuning of its electrical properties upon lattice compression by altering its grain boundary morphology, band gap structure, and relaxation frequency. Such effects have substantial significance in tuning the properties and crystalline structures for other nanomaterials as well.