Interplay of cation ordering and thermoelastic properties of spinel structure MgGa2O4

Abstract

The coefficient of thermal expansion and elastic stiffnesses of spinel structure MgGa2O4 were determined from 103 K to 1673 K using dilatometry and resonant ultrasound spectroscopy. The state of cation order was investigated on specimens quenched from temperatures up to 1473 K via single-crystal X-ray diffraction. Even at room-temperature, the material is stiffer than what was expected from DFT simulations at 0 K, however, the stiffness falls within the predicted range based on the stiffness of the constituent oxides of MgGa2O4. The anisotropy of its longitudinal elastic stiffness is low, whereas there is a high anisotropy of the shear resistance compared to other cubic materials. At about 820 K–860 K, the temperature dependences of both thermal expansion and elastic properties change rapidly. Cation reordering also starts in this temperature range; the state of order is static at lower temperatures. Thus, MgGa2O4 undergoes a glass-like transition when heated above 820 K–860 K, where the state of cation order starts relaxing towards equilibrium in laboratory timescales. Landau-theory for nonconvergent cation ordering can describe the observed cation order at elevated temperatures well.

Effects of Mg Component Ratio on Photodetection Performance of MgGa2O4 Solar‐Blind Ultraviolet Photodetectors

“…For AB 2 O 4 spinel structure, oxygen ions are cubic close‐packed, and cations occupy 1/8 of the tetrahedral sites and 1/4 of the octahedral sites. According to the previous studies, [ 28 ] MgGa 2 O 4 has a partially inverse spinel structure with an inversion index of between 0.81 and 0.87 at room temperature, indicating the disordered distribution of its metal cations. As a result, the optical, electrical, and optoelectronic properties of MgGa 2 O 4 vary significantly with the components of Mg and Ga cations.…”

Novel transparent MgGa2O4 and Ni2+-doped MgGa2O4 ceramics

“…Magnesium gallate (MgGa 2 O 4 ) is a stiff, refractory (melting point ~1930 ℃ ), double oxide, with an intermediate band gap value (~4.9 eV) that makes it possible to produce both insulator and conductive variants, as well as being resistant to decomposition until close to its melting point [1]. In its opaque state, it has various applications, including electronics, energy production, and spintronics [1,2], but the most interesting applications are those that exploit the fact that transparency (in the single crystal state) can be coupled with n-type electronic conductivity [1,3]. For instance, photodetectors, gas sensors, transparent electrodes, solid-state phosphors, waveguides, LEDs, or lasing ion hosts (operation at < 100 K) may be derived from this material [3][4][5][6][7].…”

Angular Jahn–Teller Effect and Photoluminescence of the Tetrahedral Coordinated Mn2+ Activators in Solids–A First-Principles Study

“…The first-principles calculation was performed in the framework of density functional theory (DFT) using the Vienna ab initio simulation package (VASP). , The exchange correlation functional was described by the generalized gradient approximation (GGA) of the Perdew–Burke–Ernzerhof (PBE) functional, and the interaction between ions and electrons was evaluated by the projector augmented wave (PAW) method . The lattice parameters of host crystals were relaxed using a 400 eV cutoff energy and a 5 × 5 × 5 k -point mesh, which deviate slightly from experimentally measured results by −0.27% to 0.34%, − except for the MgGa 2 O 4 crystal that deviates by 1.41% due to the large degree of Mg–Ga site inversion in the material realized in the experiment (see more details in Table S1 of the Supporting Information). Actually, it has been reported that the volume decreases as the degree of inversion increases .…”