Research On Dielectric And Piezoelectric Properties Of Lead-free Potassium Lithium Tantalate Niobate Single Crystals

With the growing development of science and technology, as a basic industryfor the development of human society, material science should keep abreast of thetimes. As large-scale application currently is lead-zirconium-titanate, piezoelectricmaterial is a major concern in recent years; for the environment and sustainabledevelopment, looking for lead-free piezoelectric ferroelectric materials to replace itis contemporary and historical mission of the researchers in the related field. In thepast ten years, there are mass exploitations of lead-free piezoelectric ceramics andtheir modification in the area of international ferroelectric, but replacing thelead-zirconate-titanate ceramics to application is too early; thus, the emphasis focuson how to further improve the performance and stability of lead-free materials.Due to its high orientation, the performance of ferroelectric single crystals isfar beyond that of the same composition of ceramics; moreover, the structure offerroelectric single crystal is simpler than that of ceramic, as well as convenient toresearch on orientation-dependent physical mechanism. Potassium tantalum niobatecrystal is a well-known solid solution in photorefractive material, the vast majorityof research is focused on the optical properties; however, systemic electricalproperties (dielectric, pyroelectric, piezoelectric and ferroelectric properties) arerarely reported. And until now, research has focused on the tantalum-rich potassiumtantalum niobate crystal; niobium-rich regions have not been studied.Thus, combining the development background of lead-free piezoelectric andferroelectric material and research status of potassium tantalate niobate crystal, andthrough analysis synthesis and compositional phase diagram of potassium tantalumniobate crystal, a series of big sized, high quality, and niobium-rich lithium-dopedof potassium tantalum niobate crystals (potassium lithium tantalum niobate singlecrystals,(K,Li)(Ta1-xNbx)O3, KLTN) have been obtained using top-seeded meltgrowth method), and then carried out their research work. The composition,structure, and thermal expansion performance of niobium-riched KLTN crystals areanalyzed. The compositions are determined using energy dispersive spectrometry(EDS); crystal structures are characterized using x-ray diffraction (XRD), and theevolution of lattice parameters and the replacement of Fe: KLTN crystals are alsoanalyzed.Dielectric property of lead-free crystals KLTN is comprehensivelycharacterized. Through dielectric performance of all compositions along differentcrystal orientation in different frequency and large temperature range, phase transition mechanism of niobium-rich KLTN crystals are determined, and all ofphase transition temperatures are obtained; poling process for dielectric property isdiscussed; diffusion characteristics of niobium-rich KLTN crystals are analyzed;dielectric tunability of KLTN crystals is characterized, and the behavior of dielectricconstant and loss under dc bias is determined.The Polarization properties of lead-free crystals KLTN are analyzed throughtheir pyroelectric and ferroelectric properties. Pyroelectric properties ofniobium-rich KLTN single crystal are determined; the phase transition points arefurther confirmed; the spontaneous polarizations in the whole temperature range arecomputed, and are compared with the total polarization obtained in themeasurement of thermal expansion. The ferroelectric P-E hysteresis loops ofniobium-rich KLTN crystals are measured, and their coercive field and the remnantspontaneous polarization are determined. Combined pyroelectric property andhysteresis loops, spontaneous polarizations have been theorically analyzed.Piezoelectric properties of niobium-rich KLTN single crystals are determined.The piezoelectric vibrators of horizontal length vibration mode, thickness vibrationmode, vertical vibration mode and horizontal shear mode of niobium-rich KLTNsingle crystals are made; piezoelectric constant and electro-mechanical couplingfactor are determined, and also compared with those of traditional piezoelectricmaterials. The vibration behavior of KLTN crystals is analyzed using ultrahighfrequency vibration meter, and the surface profile at resonant frequency is obtained.The surface morphology and ferroelectric domains of niobium-rich KLTN crystalsare observed using piezoelectric response force microscopy (PFM).