Effect of strain on the physical properties of Ni₂MSbO₆ (M = Sc, In)

First-principles calculations were carried out to understand the impact of uniaxial strain on the structural, electronic, ferroelectric, and magnetic properties of corundum double oxides Ni₂MSbO₆ (M = Sc, In) for multiferroic and piezoelectric applications. These compounds are crystallized in rhombohedral crystal symmetry with ferroelectric space group R3 no. 146. Structural relaxation revealed that these compounds have antiferromagnetic (AFM) spin ordering due to the anti-parallel alignment of magnetic cations. The applied strain significantly affects the physical properties of Ni₂ScSbO₆ and Ni₂InSbO₆. The GGA + U method was used to handle the strong electron-electron interactions and calculate their magnetic and electronic properties. These are direct band gap semiconductors having band gap values of 2.68 and 1.38 eV respectively, which lie in the visible range of the electromagnetic spectrum, enabling them functional materials for optoelectronic, transistors, and photo-detector devices. The band gap of these materials can be tuned with uniaxial strain and increase and decrease linearly under compressive and tensile strain. Mechanical parameters confirmed their stability. The calculated values of polarization and magnetic moments are 11.24/10.19 μC/cm² and 1.84/1.87 μ_B/Ni²⁺ for Ni₂ScSbO₆/Ni₂InSbO₆. The values of polarization can be reversed by externally applied strain, therefore these compounds can be used in ferroelectric devices. The thermodynamics coefficients confirm that at low temperatures, the specific heat at constant volume Cv follows Debye's law (C_v α T³), while at higher temperatures, it converges to the Dulong-Petit limit (Cv = 3 nR). The relatively low values of α and higher Debye temperature (Θ_D) indicate that the studied Ni₂MSbO₆ (M = Sc, In) possess high hardness, larger bulk moduli, and improved thermal stability and conductivity.