Study On Defect Chemistry And Dielectric Properties Of (Ba_1-xR_x)（Ti（1-x）Yb_x）O₃（R=La,Ce,Pr,Nd） Ceramics

Rare-earth metal ytterbium (Yb) usually exist in the form of Yb3+in compound,electron configuration is4f135s25p6.Yb generally belongs to the radii of atoms canreplace Ti atoms at B-sites when doped barium titanate. The rare-earth metal(La,Ce,Pr,Nd)/Yb co-doped barium titanate ceramics were synthesized using thesolid-state reaction method sintered at1400°C for12h. Crystal structure, surfacemicrostructure, dielectric properties and the defects chemical properties such as thesolid solubility were researched by X-ray diffraction (XRD), Raman spectroscopy(RS), Electron paramagnetic resonance (EPR), Scanning electron microscopy (SEM)and the Dielectric testing system technology. The results showed that Yb3+prefer toreplace Ba-sites, but with the aid of light rare-earth ions and Yb co-doped, it canrealized the Yb3+in Ti a fully occupied, then developed the high dielectric constantand low loss type Y7R dielectric stable series ceramics.The Yb-doped barium titanate ceramics were synthesized on the nominalcompositions (Ba1-xYbx)Ti1-x/4O3,(Ba1-xYbx)TiO3, Ba(Ti1-xYbx)O3,(Ba1-xYbx)(Ti1-xYbx).Discuss which site does Yb3+prefer to occupied in the ceramics, the defects chemistryand whehter the composite defects of the compensation could form in the ceramics.The results showed that can form the single-phase (Ba1-xYbx)Ti1-x/4O3ceramics when x≤0.015. Yb prefer to replace Ba-sites and forming Ti vacancy defects.Yb in otherthree types the solid solubility of BaTiO3ceramics are less than0.01. It showed thatYb did not like to occupy Ti-sites also not easy to form the compensation mode andthe oxygen vacancy defects in BaTiO3.The (La,Pr,Nd)/Yb co-doped barium titanate ceramics were synthesized namedas BLTY、BPTY、BNTY respectively. The three doping series ceramics displayedsimilar characteristics. Crystal were shown as tetragonal structure when0.01≤x≤0.03, and then shifted into cubic structure when0.04≤x≤0.05. c/a decreased andcrystal cell volume increased with increasing x. A small amount of a secondary phase(Yb2O3) appeared when x≥0.1, it showed that the solid solubility of these three typesin BaTiO3ceramics were less than0.1. The EPR spectra showed two signals at g=2.004and g=1.974respectively, thatresault by Ti vacancies and Ba vacancies. With the increase of x, Ti vacancies signaldid not change significantly, while Ba vacancies signal decreased. Higher（≥120°C）or lower (≤100°C) temperature could make both the Mn2+sextet signal and thesignals at g=2.004and g=1.974activation.The temperature dielectric spectrum showed that BLTY (x≥0.03) samples andBPTY (x≥0.04) samples composite Y5V standard. Dielectric-peak temperature (Tm)decreased rapidly at a rate of-31°C/at.%La/Yb and-22°C/at.%Pr/Yb. BNTYsamples close to Y7R standard when x=0.05. All these three types of sample showeda conductor or semi-conductor properties when x <0.03.Ce/Yb co-doped BaTiO3could not form single-phase ceramics when x≥0.02, istotally different from the above three series of (La,Pr,Nd)/Yb co-doped ceramics. Theresults show that Yb replaced Ba sites as Yb3+, and Ce replaced Ba sites as Ce4+, notform the molecular formula we designed.