Pressure effects on the metallization and dielectric properties of GaP

In situ impedance measurement, resistivity measurements and first-principles calculations have been performed to investigate the effect of high pressure (up to 30.2 GPa) on the metallization and dielectric properties of GaP. It is found that the carrier transport process changes from mixed grain and grain boundary conduction to pure grain conduction at 5.8 GPa, and due to pressure-induced structural phase transition, the resistance drops drastically by three orders of magnitude at 25.5 GPa. Temperature dependence of resistivity measurements and band structure calculations suggest the occurrence of a semiconductor-metal transition. Combining differential charge density and dielectric analysis, it is observed that the electron localization is weakened, which leads to increased polarization and larger relative permittivity in the zb structure. After the phase transition, both the polarization and the relative permittivity decrease. Pressure increases the complex dielectric constant and dielectric loss factor, due to the increase in relaxation polarization and the scattering effect of carriers. Moreover, by comparing the high-pressure behavior of GaP, GaAs and GaSb, the changes in the electronic structure and electric transport process caused by the phase transition can be understood, which can enable us to better understand the metallization behavior and dielectric properties of Ga-based III-V family semiconductors under pressure, and stimulate the design and modification of other related group III-V semiconductors for optoelectronic devices and sensors.

Abnormal Phase Transition and Band Renormalization of Guanidinium-Based Organic-Inorganic Hybrid Perovskite

Low-dimensional organic-inorganic hybrid perovskites have attracted much interest owing to their superior solar conversion performance, environmental stability, and excitonic properties compared to their three-dimensional (3D) counterparts. Among reduced-dimensional perovskites, guanidinium-based perovskites crystallize in layered one-dimensional (1D) and two-dimensional (2D). Here, our studies demonstrate how the dimensionality of the hybrid perovskite influences the chemical and physical properties under different pressures (i.e., bond distance, angle, vdW distance). Comprehensive studies show that 1D GuaPbI₃ does not undergo a phase transition even up to high pressures (∼13 GPa) and its band gap monotonically reduces with pressure. In contrast, 2D Gua₂PbI₄ exhibits an early phase transition at 5.5 GPa and its band gap follow nonmonotonic pressure response associated with phase transition as well as other bond angle changes. Computational simulations reveal that the phase transition is related to the structural deformation and rotation of PbI₆ octahedra in 2D Gua₂PbI₄ owing to a larger degree of freedom of deformation. The soft lattice allows them to uptake large pressures, which renders structural phase transitions possible. Overall the results offer the first insights into how layered perovskites with different dimensionality respond to structural changes driven by pressure.

Pressure-Induced Formation of Quaternary Compound and In-N Distribution in InGaAsN Zincblende from Ab Initio Calculation

We present the effects of In−N distribution and high pressure on the zincblende phase (0–5 GPa) of In_xGa_1−xAs_0.963N_0.037 (x=0.074, 0.111 and 0.148). Structural, electronic, and optical properties are analyzed, and it is found that non‐isotropic distribution of In−N (type C) possesses the minimum free energy for the InGaAsN conventional cell system. An increasing indium content reduces the formation enthalpy of InGaAsN. The formation enthalpy, conduction band minimum, strength of covalent bonds, and electron density differences in free space of InGaAsN are decreased under high‐pressure conditions. The dielectric performance and static permittivity of InGaAsN are lower than that of GaAs, for which the dielectric performance transforms to conductor performance at high frequency. The optimum photoabsorption coefficient is found at the composition of In_0.111Ga_0.889As_0.963N_0.037 (3In−N), which very well relates to the literature.

Pressure-induced abnormal ionic-polaronic-ionic transition sequences in AgBr

The electrical transport behavior of the superionic conductor AgBr was systematically studied under high pressure up to 30.0 GPa with electrochemical impedance spectra measurements and first-principles calculations. From impedance spectra measurements, a pressure-induced abnormal ionic-polaronic-ionic transition was found. Herein, the ionic to polaronic transition at 5.0 GPa occurs with the absence of a structural phase transition. At 8.6 GPa, the ionic state of AgBr can be reactivated after a structural phase transition. Previous structural studies based on X-ray diffraction data cannot provide strong evidence to support the ionic-polaronic transition in AgBr at 5.0 GPa. In this paper, based on first-principles calculations, a localized-electron-soup model was proposed to explain the physical origin of the ionic-polaronic transition. In this model, more localized electrons around the Br atoms are pressed into interstitial spaces and, simultaneously, polarons are formed between Ag⁺ ions and the localized electron background at 5.0 GPa. Therefore, the diffusion of Ag⁺ ions is effectively screened by the movement of the localized electron background from its equilibrium position, much like beans completely trapped in a cup of thick soup.

Pressure tuning of the thermal conductivity of gallium arsenide from first-principles calculations

Pressure tuning of the thermal transport properties of gallium arsenide.

A thermodynamic approach of self- and hetero-diffusion in GaAs: connecting point defect parameters with bulk properties

GaAs diffusion is investigated with respect to temperature and pressure using a model that interconnects point defect with bulk properties.