Internal Oxidation of Ce³⁺‐BaTiO₃ Solid Solutions

Abstract

The reoxidation process in highly Ce 3؉ -doped BaTiO 3 cerium dissolves in BaTiO 3 in oxidation state 3ϩ, independently of the starting composition. Ce 3ϩ -donor charge is comceramics was studied using TEM. Samples of two different types of solid solutions, Ba 1؊X Ce 3؉ X Ti 1؊X/4 (V؆؆ Ti ) X/4 O 3 and pensated preferentially electronically by reduction of Ti 4ϩ to Ti 3ϩ . 4 The solubility of Ce 3ϩ in BaTiO 3 during sintering in a Ba 1؊X Ce 3؉ X Ti 4؉ 1؊X Ti 3؉ X O 3 , were prepared by sintering oxide mixtures in air and in a reducing atmosphere, respectively. reducing atmosphere is much higher than in air. After sintering at 1400ЊC in a mixture of 92% Ar-8% H 2 , the solubility limit The solid solutions were reoxidized by annealing in air at of the Ba 1ϪX Ce 3ϩ X Ti 4ϩ 1ϪX Ti 3ϩ X O 3 solid solution is at X ϳ 0.52. 4 high temperatures (1000؇-1100؇C). As a result of internalIn contrast to most of the rare-earth elements which are stable oxidation of Ce 3؉ and Ti 3؉ , fluorite CeO 2 and monoclinic in air in oxidation state 3ϩ, cerium is most stable in oxidation Ba 6 Ti 17 O 40 phases were precipitated in the perovskite state 4ϩ. Cerium(III) oxide (Ce 2 O 3 ) is highly unstable and matrix. In Ba 1؊X Ce 3؉ X Ti 1؊X/4 (V؆؆ Ti ) X/4 O 3 solid solution preignites in air even at room temperature. 5 However, when it cipitates nucleate heterogeneously at grain boundaries forms stable compounds, cerium can react at high temperatures and at extended defects inside the grains, whereas in in air even in oxidation state 3ϩ (Ref. 6) (as shown also in the Ba 1؊X Ce 3؉ X Ti 4؉ 1؊X Ti 3؉ X O 3 solid solution precipitates are nuclecase of Ce 3ϩ -BaTiO 3 solid solutions). In such compounds, Ce 3ϩ ated mainly homogeneously inside reoxidized perovskite is more stable than in its oxide Ce 2 O 3 . grains. The form of the precipitates and their orientationalBecause of its low stability in air, Ce 3ϩ in solid solution with relationship with the matrix, as well as the mechanism of BaTiO 3 could be reoxidized at elevated temperatures in air. The internal oxidation, are discussed.stability of Ce 3ϩ in Ce 3ϩ -BaTiO 3 solid solutions is important for their processing, as well as for their possible applications. I. IntroductionTo our knowledge, there are no literature data on the stability of Ce 3ϩ in solid solutions with BaTiO 3 . In the present work, H IGHLY Ce 3ϩ -doped BaTiO 3 ceramics have been described the influence of reoxidation on the microstructure of Ce 3ϩ -as having promising dielectric properties, such as relaBaTiO 3 solid solution was studied using transmission electron tively high permittivity and high endurance. They can be used microscopy. as materials for the production of multilayer ceramic capacitors. 1 Cerium can exist in two oxidation states, 4ϩ and 3ϩ. It can II. Experimental Procedure be incorporated into the BaTiO 3 perovskite lattice substitutionCeramic samples of two types of solid solutions, Ba 1ϪX -ally in both existing oxidation states. In oxidation state 4ϩ it Ce 3ϩ X Ti 1ϪX/4 (V٣ Ti ) X/4 O 3 and Ba 1ϪX Ce ...

Sol–gel synthesis and characterization of Ce doped-BaTiO3

“…On the other hand, CeO 2 is partially reduced and cerium enters into the BaTiO 3 lattice as a donor at the Ba sites, when BaTiO 3 is sintered in air together with CeO 2 and an excess amount of TiO 2 . 5 Various methods such as conventional solid state reaction, coprecipitation, hydrothermal technique and sol-gel have been utilized for the fabrication of ferroelectric BaTiO 3 bulk powder and ceramics. 6 The sol-gel process is an excellent technique for formulating new compositions due to the possibility to control the stoichiometry and homogeneity of the resulting material.…”

Low-frequency dielectric spectroscopy of BaTiO3:Ce3+ceramics

“…However, Ce maintains its valence states in compounds in normal conditions, and can be changed only in special situations. [9] Dielectric measurements seem to indicate that for low-level doping of the BT structures with various dopants, frequently a diffuse phase transition (DFT) is observed. [12] For high-level doping, many of the substitutions finally lead to a relaxor behaviour of the obtained materials.…”

Effect of uniform and periodic doping by Ce on the properties of barium strontium titanate thin films

“…[10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. Ce can exist as Ce 3+ or Ce 4+ depending on the precursor used and the processing temperature.…”