Glass formation and crystallisation behaviour of yttrium aluminium tetraborate glass-ceramic
The phase diagram of the binary Y2O3–B2O3 system has been revised, the phase diagram in the pseudo-binary YAlO3–YBO3 system has been constructed and two binary eutectics have been revealed. A new ternary eutectic between YAlO3, YBO3 and an unknown ternary yttrium aluminium compound has been revealed. Glass forming ability in the ternary Y2O3–Al2O3–B2O3 system has been investigated and a glass forming diagram dependant on melt casting procedure has been determined. The expanded glass formation area occupies fields of composition with low liquidus, formed between binary yttrium aluminate, yttrium borate and yttrium aluminium borate eutectics. The crystalline phase formation in yttrium aluminium tetraborate have been determined by solid state sintering and by devitrification of the corresponding glass composition in powder, bulk and tape form. The binary aluminium and yttrium borates are formed as the first step (750–850°C) of solid state sintering and all forms of glass devitrification. Differential thermal analysis and x-ray diffraction showed the dominant ternary yttrium aluminium tetraborate phase formation at 1000–1135°C in solid sintering batches and glass powder crystallisation. This phase is formed in the range 800–950°C for bulk glass and tape crystallisation. The glass ceramics based on yttrium aluminium tetraborate are ferroelectric, with remanent polarization equal to 0·08–0·3 μC/cm2 at external field 200–240 kV/cm.
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Document Type: Research Article
Publication date: August 1, 2009