Preparation And Properties Of PLN-based Antiferroelectric Energy Storage Materials

As an important member of Pb(B'1/2B1/2")O3 family, Pb(Lu1/2Nb1/2)CO3 (PLN) received much attentions in the past few years, however, the value of energy storage density was quite low (about 0.6 J/cm3). Therefore, it is necessary to modify PLN ceramics to improve its energy storage density. In addition, single crystals with certain orientations could exhibit much superior electrical properties than the crystallographic isotropic ceramics. However, the relevant report on PLN single crystal is still quite less until now and these intrigued us to investigate the La3+-modified PLN AFE single crystals.LaxPb1-3x/2(Lu1/2Nb1/2)O3 antiferroelectric (AFE) ceramics with compositions of x = 0, 0.01,0.02,0.03,0.04,0.05 were successfully prepared by traditional solid state reactions and characterized by means of X-ray diffraction (XRD), AFE and dielectric measurements. The effects of La3+ content on the properties of the ceramics are discussed. The maximal value of the dielectric constant (?') and the Curie temperature (Tc) both gradually decrease from 662 to 356 and 272 ? to 240 ? respectively with increasing La3+content from 0 to 0.05. The electric field at which the material transitions from the AFE phase to ferroelectric (FE) phase increases along with increasing La3+ content and the maximum value of energy storage density is estimated to be 3.85 J/cm3 at 200 ? based on the unsaturated double hysteresis loops. These results indicate that La-doping is an effective method to improve the energy storage density of the Pb(Lu1/2Nb1/2)O3 AFE ceramics.It is a non-equivalence replacement when Pb2+ (0.149 nm) were replaced by La3+ (0.136 nm) with smaller radius and led to arise of lead vacancies. In order to ascertain the modification mechanism of the La3+ addition, there must be a new doping element to fill lead vacancies. Therefore, (NaxLaxPb1-2x)(Lu1/2Nb1/2)O3 antiferroelectric ceramics (x = 0, 0.01,0.02,0.03,0.04,0.05) were successfully obtained by solid state reactions. The structural phase transitions and the electrical behavior have been investigated. XRD analysis indicates that La3+ and Na+ have diffused into the lattices and the ceramics display a pure perovskite structure. It is found Curie temperature Tc for AFE transition decreases from 270 ? to 242 ? with increasing of Na+ and La3+ content, similarly, the dielectric constant (?') decreases from 677 to 390. Compared to LaxPb1-3X/2(Lu1/2Nb1/2)O3 AFE ceramics, the energy storage performance was enhanced about 7%, and the maximum value of energy storage density was calculated up to 4.12 J/cm3 at 200 ?.High quality antiferroelectric single crystal La0.011Pb0.984(Lu1/2Nb1/2)03 (La-PLN) was successfully obtained. The crystal structure adopts an orthorhombic phase and two sets of superlattice reflections due to B-site ordering and anti-parallel cation displacement are observed clearly and distinguished by the X-ray diffraction patterns. The Curie temperature Tc is near 221 ? with a low dielectric constant (about 371). The energy storage density is decreasing along with increasing temperature and the maximum energy storage density is up to 5.03 J/cm3 at 25 ?, which is good for bulk polar materials and much higher the La-modified PLN ceramics.