Thermodynamics and kinetics of cation ordering in MgAl₂O₄spinel up to 1600 degrees C from in situ neutron diffraction

Si-Disordering in MgAl2O4-Spinel under High P-T Conditions, with Implications for Si-Mg Disorder in Mg2SiO4-Ringwoodite

“…However, all these conclusions were drawn from the experimental data collected on quenched samples or based on some crystal structural features established for ambient P. In the former cases, the cation disorder information of the Rw at high P might be completely lost. In analogy to the well-known partial preservation of the high-T equilibrium state of the Al-Mg disorder in the MgAl 2 O 4 -Sp after quenching [42,53], reordering the Si and Mg cations in the Mg 2 SiO 4 -Sp presumably happens fast and proceeds towards its completion as the high-P synthesizing experiment quenches. In the latter cases, the bond length systematics and structural features established for ambient P might not be applicable to the high-P structures.…”

“…There has been excellent agreement on the T effect on the Mg-Al disorder process of the MgAl2O4-Sp at ambient P: x increases as T increases [42,47,48,50,51,[53][54][55][56][57]. As to the P effect at ambient T, discrepancy presumably exists because the order-disorder reaction could not be readily activated and did not adequately approach its equilibrium during the course of a conventional high-P study [52,90,91].…”

“…With a relatively small size difference between the Mg and Al cations in the MgAl2O4-Sp, the cation disorder achieved under high P-T conditions can be partially preserved [42,45,48,50,51,53]. In contrast, the relatively large size difference between the Mg and Si cations in the Rw may strengthen this size-dependent site preference and accelerate the cation-redistribution process during cooling, so that the cation disorder attained under high P-T conditions can be easily lost, leading to null signals for cation disorder, as observed experimentally [61,64].…”

Hydrogen and deuterium diffusion in non-stoichiometric spinel

“…The structure can be described as an ideal cubic close-packed array of O anions in which cations occupy 1/8 of the tetrahedral and ½ of the octahedral interstices. In an ideal fully ordered spinel T (tetrahedral) sites and M (octahedral) sites are occupied by X and Y cations, respectively, although in practice, spinel group minerals are characterised by varying degrees of cation disorder and mixing of X and Y over both sites, especially at elevated temperature [17]. In fully ordered, stoichiometric spinel, MgAl 2 O 4 ('ideal spinel'), Mg fully occupies T sites and Al fully occupies M sites.…”

Electronic and optical properties of the spinel oxides MgxZn1-xAl2O4 by first-principles calculations

“…They are widely used in various fields such as catalysis, gas sensor, semiconductor, biomedical, catalyst carrier, as well as electroluminescent displays owing to their catalytic, physical, structural, electronic and optical properties. 1,2 Among them, MgAl 2 O 4 and ZnAl 2 O 4 have high-temperature resistance, 3,4 and they are highly reflective for wavelengths in the ultraviolet (UV) region, which make them candidate materials for reflective optical coating in aerospace applications. 5 In particular, MgAl 2 O 4 is one of the potential candidates for the full wave band transparent window materials with high transmittance in IR-and visible-wavelength even extending to microwave ranges, 6,7 and it also can be used as lamps and lasers, 8 transparent ceramic material for high-temperature, 9 transparent armor and glass.…”