In this paper, potassium sodium niobate lead-free piezoelectric thin films were prepared by sol-gel method. The electric domain structure and optical band gap of the thin films were regulated by doping Mn. It is found that Mn doping increases the grain size and density of KNNLT piezoelectric film surface. In addition, Mn doping can regulate the electric domain of thin films. Increasing Mn doping concentration can regulate the size and distribution of electric domain, and the ratio of 71 degrees electric domain increases with the increase of doping concentration. The results show that the optical band gap decreases gradually with the increase of doping amount when the annealing temperature is 650 degrees C. The lowest optical band gap reaches 3.426 eV, and is lower than the undoped KNNLT films.

In this paper, Bi2O3-doped (K0.5Na0.5)NbO3 (x = 0.1, 0.2, 0.3, 0.4) lead-free ceramics are prepared by a conventional solid-state reaction and analyzed by studying the structure, ferroelectric, and piezoelectric properties. It is found that the doping of Bi2O3 increases the proportion of the trigonal phase in KNN ceramics, thus enabling the construction of KNN ceramics with an orthogonal–trigonal phase boundary at room temperature. At the same time, doping with Bi2O3 can reduce the grain size and improve grain size uniformity of the ceramics. The KNN-0.1%Bi2O3 ceramic has the best piezoelectric properties in all composition; the results are as follows: d33 = 121pC/N, kp = 0.474, kt = 0.306.

In this work, the influence of temperature on phase structure, dielectric property and domain structure of (K,Na)(Nb,Ta)O-3 (KNNT) crystal from 20 to 200 degrees C was studied. The irreversible domain wall motion of single crystal is strongest at phase transition temperature by Rayleigh analysis of dielectric properties. The domain structure in the heating and cooling process of single crystal was observed by means of piezoelectricity microscope. The domain structure changed obviously with temperature and the domain structure change is particularly prominent at the phase transition temperature.

Structural, ferroelectric, dielectric, and piezoelectric properties of K0.5Na0.5NbO3-LiTaO3-xmol%MnO2 lead-free piezoelectric ceramics with 0.0 ≤ x ≤ 0.3 were studied. The ceramic samples were synthesized through the conventional solid-state reaction method. The MnO2 addition can reduce the sintering temperature of KNLNT ceramics. Compared with undoped KNLNT ceramic, the piezoelectric measurements showed that piezoelectric properties of K0.5Na0.5NbO3-LiTaO3-xMnO2 were improved (d33 = 251 pC/N) when x = 0.1. In addition, KNLNT-xMnO2 ceramics have larger Pr(20.59~21.97 μC/cm2) and smaller Ec(10.77~6.95 kV/cm), which indicates MnO2 has excellent softening property, which improves the ferroelectric properties of KNLNT ceramics This work adds relevant information regarding of potassium sodium niobate K0.5Na0.5NbO3 (KNN) when doped Li, Ta, Mn at the B-site.