Microstructure and piezoelectric properties of Ho2O3 doped (K0.4Na0.6)0.95Li0.05Nb0.95Sb0.05O3 lead-free ceramics near the rhombohedral-orthorhombic phase boundary

Ho2O3 doped (K0.4Na0.6)(0.95)Li0.05Nb0.95Sb0.05O3 (KNLNS) lead-free piezoelectric ceramics were prepared by normal sintering to construct rhombohedral-orthorhombic polymorphic phase boundary. An orthorhombic and rhombohedral phase boundary is formed in the ceramics around x = 0.6-0.8, indicating that the doping of Ho2O3 is helpful to stabilize the low temperature rhombohedral structure. The surface and interior of the x a parts per thousand currency sign 0.6 samples exhibit tetragonal and orthorhombic structures, respectively, which demonstrate that phase transitions can be induced by the alkali metal oxides volatilization during sintering. Anomalous broad dielectric relaxation is observed in the epsilon (r)-T curves near T (C) when x a parts per thousand yen 0.8. Abnormal grain growth occurs when small amount of Ho2O3 is added but the grain size decreases at high amount of Ho2O3. The optimum electrical properties of d (33) = 252 pC/N, k (p) = 39.67 %, epsilon (r) = 930.4, and Q (m) = 59.5 are obtained at x = 0.6. These results show that the KNLNS ceramic with 0.6 wt% Ho2O3 is a promising lead-free piezoelectric material.