Critical Evaluations and Thermodynamic Optimizations of the MnO-Mn$$_{2}$$O$$_{3}$$-SiO$$_{2}$$ and FeO-Fe$$_{2}$$O$$_{3}$$-MnO-Mn$$_{2}$$O$$_{3}$$-SiO$$_{2}$$ Systems

Abstract

The crystal structure of annealed chevkinite-(Ce), ideally (REE,Ca) 4 Fe 2+ (Ti,Fe 3+ ,Nb) 4 Si 4 O 22 , monoclinic, C2/m, crystal (2 an) a 13.400(1), b 5.7232(4), c 11.0573(9) Å, 100.537(2)°, V 833.7(2) Å 3 and crystal (3 an) a 13.368(2), b 5.7243(6), c 11.041(1) Å, 100.516(1)°, V 830.7(2) Å 3 ; Z = 2, from Mongolia, has been solved by direct methods and refined to R 1 values of 6.3 and 5.7% using 1287 and 1180 unique (|F o | > 4F) reflections collected with a single-crystal diffractometer and MoK radiation. Electron-microprobe analysis gave: crystal (2 an) based on 13 cations per formula unit. Infrared spectra of unannealed crystals suggest significant radiation-induced damage. The structures of two unannealed crystals were refined, but there are major discrepancies (~13%) between the sums of the site-scattering values at the octahedrally coordinated M sites and the analogous values calculated from the chemical compositions determined by electron-microprobe analysis. These discrepancies were not present when data were collected on annealed crystals, indicating that the original crystals are partly metamict and that this can significantly affect the results of site-scattering refinement. In the crystal structure of chevkinite, there are two distinct (SiO 4) tetrahedra that share one vertex to form an [Si 2 O 7 ] group: <Si-O> = 1.614 (2 an) and 1.612 (3 an) Å, <Si(1)-O(8)-Si(2)> = 172.0° (2 an) and 170.6° (3 an). There are four octahedrally coordinated M sites that are occupied by small-to medium-sized divalent to pentavalent cations. The M(1) site is occupied dominantly by Fe 2+ with minor Mn 2+ , and the M(2), M(3) and M(4) sites are occupied by Ti, Fe 3+ and Nb. There are two A-sites that are occupied by REE and minor Ca and Th, with <A-O> = 2.56 (2 an) and 2.55 (3 an) ([8]-coordinated) and 2.66 (2 an) and 2.55 (3 an) Å ([10]-coordinated). There are two crystallographically distinct rutile-like chains of octahedra ([M(3) + M(4)] and [M(2) + M(2)]) that extend in the b direction and link to form a layer of octahedra parallel to (001). The layers of octahedra link through [Si 2 O 7 ] groups to form a framework with two interstitial A sites, CN = [8] and [10], in which Ce is dominant over other REE, Ca and Th.

Numerical Treatment of Oxide Particle Dissolution in Multicomponent Slags with Local Gibbs Energy Minimization

“…These thermochemical calculations are performed using a newly developed Gibbs energy minimization algorithm in combination with an in‐house thermochemical database built on the modified quasi‐chemical model for the description of the liquid phase. [ 31–43 ] For a deeper discussion on the Gibbs energy minimization method, see, for example, refs. [29,30,44–49].…”

Calphad Modeling of LRO and SRO Using ab initio Data

“…S is also prone to capture electrons and compounds with F, Cl etc are also strongly ionic but there are fewer solution phases with these elements. There has been several assessments for different oxide systems using CEF-for example, [56][57][58][59][60][61][62][63] using both experimental and DFT data.…”

Effect of transition metals (MO-TiO2, MnO2, Fe2O3, and ZnO) on crystallization and electrical conductivity of SiO2–CaO–Na2O–P2O5-based glass-ceramics

“…TM ions in glasses are center of attraction due to their variable oxidation states and intermediate nature of TM oxides in glasses [8]. TM ions have ample chances to exhibit wide range of oxidation states due to partially filled d-orbitals.…”