Core‐Shell Structure Formation in Nb₂O₅‐Doped SrTiO₃ by Oxygen Partial Pressure Change

Abstract

A core-shell structure was observed in SrTiO 3 doped with 1.2 mol% of Nb 2 O 5 , after sintering in a reducing atmosphere (5H 2 -95N 2 ) and then in an oxidizing atmosphere (air). In undoped and Al 2 O 3 -doped SrTiO 3 specimens, no core-shell structure formed after the same sintering treatments as those for SrTiO 3 doped with 1.2 mol% of Nb 2 O 5 . The measured chemical compositions of the core and shell regions of 1.2-mol%-Nb 2 O 5 -doped SrTiO 3 grains showed that the Sr/(Ti + Nb) ratio of the shell regions grown in air was ∼1% less than that of core regions grown in 5H 2 -95N 2 , which was in good agreement with a value predicted by available defect equations. Therefore, the observed coreshell structure is thought to result from the formation of strontium vacancies in an oxidizing atmosphere.

Structure and Microwave Dielectric Behavior of A‐Site‐Doped Sr(1−1.5x)CexTiO3 Ceramics System

“…The solid solubility limits of ceria in ST ceramics were expected to be quite small because of the significant difference between the ionic sizes of Sr 2+ ( r Sr 2+ = 1.44 Å) and Ce 4+ ( r Ce 4+ = 0.87 Å). It was reported that, the lower solubility of donor doping like CeO 2 , La 2 O 3 , and Nb 2 O 5 in BaTiO 3 and SrTiO 3 ceramics is primarily due to the formation of core–shell‐structured fine grains and/or layered intergrowth compounds. In contrast to this phenomenon, the decrease in the lattice parameters with the addition of ceria indicated that the lower solubility of ceria in SrTiO 3 is not due to the formation of core–shell‐structured fine grains and/or layered intergrowth compounds.…”

Effect of Sintering Atmosphere on Grain Boundary Segregation and Grain Growth in Niobium‐Doped SrTiO3

“…Another cause for the negative charge distribution at grain boundaries in H 2 may be trapped electrons. In highly reducing atmospheres, not only the extrinsic electrons compensating for the excess charge of donor dopants 43,45,46 are formed but also a number of intrinsic electrons for the compensation of oxygen vacancies caused by low oxygen partial pressure. 42,43 If a fraction of these electrons is trapped at a new set of interface electronic states, which is considerably different from those of the bulk, 47 they can contribute to the negative boundary charge.…”

Influence of Sr/Ti Stoichiometry on the Densification Behavior of Strontium Titanate

“…The materials are widely used in electronic industry, e.g., as positive temperature coefficient resistors, capacitors, or piezoelectric transducers. In all these applications the control of the microstructure during processing is highly important because the electrical properties are widely governed by the grain boundary regions 1,2 and by grain size, which becomes especially clear in the example of grain boundary barrier layer capacitors 3,4 . This study focuses on strontium titanate as model material because its bulk defect chemistry is well known through a multiplicity of studies in the literature.…”