Ba₂Ti₉O₂₀ Phase Equilibria

Abstract

The heterogeneous phase distribution found in Ba2Ti9OZ0 ceramic resonators results from a temperature-dependent phase boundary and slow reaction kinetics. When sintered at 1350°C or higher in oxygen the BaZTi9OZ0 phase becomes slightly reduced and barium-rich. Thus a stoichiometric composition forms rutile and "BazTi902:' phase. On slow cooling the excess barium diffuses to the oxygen-rich surface where it reacts to form an envelope of rutile-free material surrounding a core containing a small amount of rutile.

Effect of second-phase particle morphology on grain growth kinetics

“…Furthermore, as in the original Zener theory, essentially all existing studies focus on the effects of the volume fraction and average size of second-phase particles on the final pinned size of the matrix grains. In reality, the morphology of second-phase particles can be rather complicated, ranging from spherical to plate-like and needleshaped [4,8]. As pointed out by Nes et al [5], the morphology of second-phase particles significantly affects the magnitude of pinning forces acting on a moving grain boundary.…”

Preparation of BaTi<SUB>2</SUB>O<SUB>5</SUB> Single Crystal by a Floating Zone Method

“…TiO 2 rich BaO-TiO 2 system compounds such as BaTi 4 O 9 3,4) and Ba 2 Ti 9 O 20 3, 5,6) are also expected as dielectric materials to be used at microwave frequencies. However, no report has been published on the compound having higher permittivity than those coumpounds in the BaO-TiO 2 system.…”

A re-look at critical factors influencing single-phase formation of Ba2Ti9O20 microwave dielectrics

“…It is well recorded in literature that formation of 2 : 9 as a singlephase material is very difficult (O'Bryan and Thomson 1983;Wu and Wang 1988;Wang et al 2003). Many theories have been proposed to explain the difficulty of formation of single-phase 2 : 9.…”

“…Many theories have been proposed to explain the difficulty of formation of single-phase 2 : 9. Jaakola et al (1980) andThomson (1983) feel that the formation of 2 : 9 is limited basically by the diffusion of ions. Wu and Wang (1988) argue that it is the thermodynamic factors such as high nucleation energy and surface energy associated with the formation of 2 : 9, which limits its formation and growth as single-phase material.…”