Pressure induced band-gap tuning in KNbO3 for piezoelectric applications: Quantum DFT-GGA approach

Under pressure KNbO3 has been studied for its structural, electronic and mechanical properties by using state of the art density functional theory. Elastic stability criterion and structural optimizations show stable cubic phase, up to 150 GPa, of the studied compound. Moreover the compound undergoes brittle (indirect band-gap) phase transformation to ductile (direct band-gap) phase transformation while retaining its cubic phase. Anisotropy is observed to decrease with pressure which results in an increase in the value of piezoelectric coefficient and thermal conductivity. The electronic properties reveal that anti-ferromagnetic nature remains invariant with increase in pressure. But Cauchy pressure explains that the majority of covalent bonds in unit cell are shifted towards ionic bonding at higher pressures. Our results are predictions for applications of KNbO3 in high pressure optoelectronic devices and sensors.