Al3+-doping dependence on structural phase evolution in the LaCrO3 compound studied using atomistic simulation

Abstract

We report the atomistic simulation study of the Al3+-doping effects on the structural properties of LaCrO3 compound. We observed that Al3+-doping in the range of 0-80 wt% induced a decrease in the lattice parameters, unit cell volume, and Cr/Al-O and La-Cr/Al bond lengths. At the phase transition, around 60 wt% of Al3+-doping, and positive volume expansion was observed, which confirmed the orthorhombic (Pnma) to rhombohedral (R-3c) phase transition. The volume decompression amount was calculated to be about +0.50 Å3 (+33.33%) per formula unit. The elastic constants of the unit cell expansion increased as Al3+-doping increased 80 wt%, and were estimated to be C11=C33, C12/C21=C23/C32, and C44=C66 for the orthorhombic and rhombohedral phases, respectively. However, these constant values match to those of the rhombohedral structure for further Al3+-doping. Thus, we concluded that increasing substitution of Cr3+ (0.615 Å) by Al3+ (0.535 Å) in the LaCrO3 lattice induces a decrease of distortions at (Cr/Al)O6 octahedra, indicating that a reduction of the chemical pressure caused the structural phase transition.