Fabrication of BaTi₂O₅ Glass−Ceramics with Unusual Dielectric Properties during Crystallization

Abstract

A 2-mm-diameter glass sphere of ferroelectric BaTi2O5 was fabricated from melt using containerless processing. The glass structure was analyzed by high-energy X-ray diffraction using an incident photon energy of 113.5 keV, indicating that distorted Ti−O polyhedra, with average coordination number (N Ti - O) of approximately 5, presented in the glass. Above the glass transition temperature (972 K), three successive phase transitions, from glass to a metastable α phase at 972 K, then to a metastable β phase at 1038 K, and finally to a stable monoclinic γ phase above 1100 K, were observed. At the crystallization temperature of the α phase, the permittivity jumped instantaneously by more than 1 order of magnitude, reaching a peak of 1.4 × 107. This interesting phenomenon, occurring near the crystallization temperature, has important technical implications for obtaining an excellent dielectric glass−ceramic through controlled crystallization of BaTi2O5 glass.

Thermal and optical properties of glass and crystalline phases formed in the binary R2O3-Al2O3 (R = La-Lu and Y) system

“…[36][37][38][39][40][41][42] However, in most of these binary systems, eutectic compositions have been selected to study the glass forming ability. This condition makes glass formation easier because molecular ordering can be suppressed and the amorphous structure can be maintained by instantaneous phase transition.…”

“…Recently, some binary systems, such as TiO 2 -, Nb 2 O 5 -and WO 3 -based glasses, have been vitrified in bulk form without using any network-former oxides by containerless processing. [36][37][38][39][40][41][42] This indicates that containerless processing is a new vitrification technique that uses the melting and solidification processes. Furthermore, containerless solidification under deep undercooling conditions can achieve novel microstructures such as refined grain size, stable/metastable phases, and glassy phases.…”

“…A levitation technique could provide a new method for phase selection, because the lack of a heterogeneous nucleation site as crucible wall makes it easy to achieve deep undercooling. [36][37][38][39][40][41][42][43] Therefore, containerless processing is useful for vitrifying materials with low glassforming ability. 33 Herein, we focus on the RAlO 3 system without using network-former oxides, because the glass-forming region, a)…”

Preparation and property of BaTi2O5 ceramics by arc-melting and spark plasma sintering

“…Unfortunately, BaTi 2 O 5 was reported to be easily decomposed into BaTiO 3 and Ba 6 Ti 17 O 40 [8][9][10], and difficult to synthesize by the conventional solid-state reaction. Although the processes of sol-gel [11,12], hydrothermal reaction [13], containerless processing [14], rapid cooling [15,16], floating zone [17,18], arc-melting [19] have been developed to prepare singlephased BaTi 2 O 5 in forms of micro-powders, nano-belts, glass spheres, needle-like or rod-like crystals, both the densification and dimension of those products are not satisfied. For the purpose of practical and wider applications, dense and large-scaled BaTi 2 O 5 ceramics should be produced, especially as the target materials for further preparing BaTi 2 O 5 films by physical vapour deposition.…”

Thermal, mechanical, and upconversion properties of Er3+/Yb3+ co-doped titanate glass prepared by levitation method

“…In the past several years, some efforts were made for fabrication of bulk titanate glasses through levitation method [17][18][19]. And their dielectric and refractive behavior have been investigated [20][21][22]. But to the best of our knowledge, there is still no report on upconversion property of bulk titanate glass.…”