Study On Defect Chemistry Associated With Site Occupation Of Dy In The BaTio₃ Lattice

This experiment is mainly to study changes of the crystal structure and related chemical defects by adding single doped or double doped Dy in barium titanate. Using XRD, SEM, EDS, EPR, RS and the microscopic analysis methods such as dielectric test system to discuss the modified behaviours and microscopic compensation mechanism of single admixture (Ba1-xDyx)(Ti1-xDyx)03 and mixed series of (Ba1-xLax)(Ti1-xDyx)03, (Ba1-xDyx)(Ti1-x/2Cax/2)O3 (Ba1-xRx)(Ti1-xDyx)03 (R=Eu、Gd、Tb) ceramics. Finally, dielectric materials of a high dielectric Y5V and dielectric temperature stable X8R were made. At the same time, the solid solubility, site occupation, phase structure and surface morphology of (Ba1-xDyx)Ti1-x/4O3 (x= 0.01) ceramics with different sintering temperatures also were studied.The solid solubility in the compensation mode of (Ba1-xDyx)(Ti1-xDyx)O3 ceramics was determined to be x=0.07. With the increase of x, dielectric behaviors were changed from the first phase transition to a diffusion phase and into a high dielectric temperature stable Y7R specification. A very strong g=1.974 EPR signal associated with ionized Ba-vacancy defects appeared in intentional designed single-phase (Ba1-xDyx)Ti1-x/4O3 ceramics. The (Ba1-xDyx)Ti1-x/4O3 ceramics can be expressed as a real formula is (Ba1-xDy3x/4)(Ti1-x/4Dyx/4)O3.The solid solubility of LaBa-DyTi defect complexes in the BaTiO3 lattice was determined to be x=0.17. With an increase in x, the increase in the unit cell volume was linear and satisfied Vegard’s law. The Tm decreased rapidly at a rate of -23℃/at.% LaBa-DyTi. The BLTD ceramics with x=0.05 and 0.07 met the Y5V specification. A weak g =2.004 EPR signal associated with ionized Ti-vacancy defects appeared in all of the BLTD ceramics. The exclusive occupations of La3+ ions at Ba sites and the preference for the self-compensation mode by Dy3+ ions are responsible for the formation of predominant LaBa-DyTi defect complexes and the appearance of the minute concentration of Ti vacancies and LaBa-DyTi defect complexes.The solid solubility of (Ba1-xDyx)(Ti1-x/2Cax/2)O3 (0.04< x< 0.30) (BDTC) ceramics is x = 0.15. The unit cell volume of the BDTC ceramics overall show a increasing trend with the increase of x. when x is less than 0.08, the temperature of the dielectric peak gradually moved towards the low temperature with the increase of the doping content. A weak g=2.004 EPR defect signals are appeared in all BDTC ceramics.When x=0.06. (Ba1-xRx)(Ti1-xDyx)O3 (including:R=Eu, Gd, Tb) ceramics were fully integrated into BaTiO3 lattice and formed a solid solution. In the Eu/Dy co-doped ceramics, Eu ions had a mixed valence Eu3+ and Eu2+ in the BaTiO3, some of the Dy3+ were inevitably set into the Ba-site. Ag= 1.984 signal seen as a Gd3+ was observed in the BaTiO3 ceramics doped with Gd/Dy. In the TD6 ceramics, some of Tb replaced the Ti-site in the form of Tb4+ and accompanied a small amount of Dy3+ in the Ba-site.With the increase of sintering temperature and dopant in (Ba1-xDyx)Ti1-x/4O3 (x= 0.01) ceramics, the diffusion degree increased and favorabled for diffusion of Dy from Ba-site into the Ti-site, which eventually caused a larger unit cell volume. Sintering temperature did not affect the phase structure of BD1AT.