Point defect structure of La-doped SrTiO3 ceramics with colossal permittivity

Abstract

Sr 1-x La x TiO 3 (SLTO) ceramics with colossal permittivity were fabricated by conventional solid-state reaction method. The point defects of pure STO and SLTO ceramics were analyzed by Positron Annihilation Lifetime Spectroscopy (PALS) and Coincidence Doppler Broadening (CDB). The charge compensation mechanisms and dielectric properties of ceramics were investigated. The results indicated that the intrinsic defects in pure STO ceramics were mainly. The charge compensation mechanism of SLTO ceramics was predominantly formation of. With increasing La content, ε r of SLTO ceramics increased up to ~70000 at room temperature. The results of first-principle calculations indicated that the colossal permittivity came from a sharp polarization increase caused by dipole structure of defects. tanδ of SLTO ceramics showed obvious Debye relaxation at high temperatures and the relaxation showed a multiple relaxation times derived from different kinds of polarization mechanism. The main polarization mechanism of SLTO ceramics gradually changed from ion displacement polarization to defect dipole polarization influenced by the concentration of La dopants.

Effect of cation vacancies on the optical and dielectric properties of KSr2Nb5O15: A first‐principles study

“…To maintain neutrality, the electron compensation mechanism and vacancy compensation are both considered. 21 Table 1 shows the lattice constants of KSN, KSN-K, KSN-Sr, and KSN-K&Sr For KSN-K, KSN-Sr, and KSN-K&Sr, the lattice constant a ≠ b. KSN with vacancies tends to have orthorhombic structures from tetragonal structures, consistent with the reported calculation results of La 3+ doped KSN by first principles 22 and experimental results of Bi 3+ doped in KSN. 23 La 3+ and Bi 3+ doped in KSN generate cation vacancies, which causes distorted lattice structures and increased polar nanoregions.…”

“…The experimental results in this paper are consistent with the calculated results in terms of regularity that the dielectric constant of KSN‐K(KSN‐4Sr) is smaller than that of KSN‐Sr (KSN‐4K) and KSN‐K&Sr (KSN), demonstrating that the effect of the intrinsic defects play the main role in dielectric constant. Our previous work showed that cation vacancy would increase the polarization of the perovsktie lattice . Because the charge of Sr 2+ is larger than that of K + , Sr 2+ vacancy showed more influence for polarization than K + vacancy, which indicates that KSN with K + vacancy (corresponding to KSN‐4Sr sample) should show relative smaller dielectric constant.…”

“…Equations represent the coexistence of one K + vacancy and one Sr 2+ vacancy in the KSN lattice structure. To maintain neutrality, the electron compensation mechanism and vacancy compensation are both considered …”

“…Our previous work showed that cation vacancy would increase the polarization of the perovsktie lattice. 21 Because the charge of Sr 2+ is larger than that of K + , Sr 2+ vacancy showed more influence for polarization than K + vacancy, which indicates that KSN with K + vacancy (corresponding to KSN-4Sr sample) should show relative smaller dielectric constant. Figure 13 shows the transmittance of the KSN, KSN-4K, and KSN-4Sr ceramics.…”

TiO2–SrTiO3 Biphase Nanoceramics as Advanced Thermoelectric Materials

“…At the same time, concentrating limited electron-carriers occur most likely on TiO 2 /SrTiO 3 interfaces as in the most loose, defect regions of TiO 2 and SrTiO 3 crystallites. On the other hand, the results of [176] indicate that intrinsic point defects in the pure SrTiO 3 ceramics are mainly V Ti ′′′′. Probably, V O ′′ will be associated with a cation vacancy forming (V Ti ′′′′ + 2V O ′′) complex, namely, the Shottky defect.…”