The structural, elastic, piezoelectric, and electronic properties of K1−xMxNbO3 (M = Li, Na) were investigated by first-principles calculations. The results show that the modifications have effects on the elastic properties of KNbO3 and strengthen the anisotropy. Na and Li doping can slightly improve the piezoelectric stress tensor (e33) and piezoelectric strain tensor (d33) of KNbO3. With the increase in the x value from 0 to 0.5 in K1−xMxNbO3, the d33 value is improved from 24.4 to 36.3 pC/N (M = Na) and 41.5 pC/N (M = Li), and the piezoelectric property is improved by 1.49 and 1.70 times with the modifications of Na and Li, respectively. This conclusion is consistent with the result of Born effective charge and band structure results. The Born effective charge average values (Z*̄) for K and Nb atoms in K0.5M0.5NbO3 (M = Li, Na) are slightly increased compared to those in KNbO3. KNbO3 has an indirect bandgap, while Na and Li doping makes K0.5Na0.5NbO3 or K0.5Li0.5NbO3 a direct bandgap semiconductor. This study may provide a theoretical insight into Na and Li modified KNbO3 for their piezoelectricity.
