From eulytine to the ambidextrous crystal via the amorphous route: Lead & calcium bismuth germanate glasses
1975; Elsevier BV; Volume: 10; Issue: 1 Linguagem: Inglês
10.1016/0025-5408(75)90142-7
ISSN1873-4227
Autores Tópico(s)Mineralogy and Gemology Studies
ResumoLead and calcium bismuth germanate glasses containing at least 40 mole% GeO2 were prepared. Physical properties and infrared spectra suggest that for glasses close to the PbO · Bi2O3 · 2GeO2 composition: (a) packing efficiency is directly dependent upon cation size, (b) refraction is dependent upon cation type, (c) calcium can substitute for lead in nearly ideal fashion, (d) the open eulytine arrangement of a 2Bi2O3 · 3GeO2 glass has collapsed, and (e) Ge2O7 dimers and small chains of GeO4 tetrahedra (characteristic of Pb5Ge3O11 and PbGeO3 respectively) may persist. These findings offer a rationale for the limited yields of Ca3Al2Ge3O12 garnets obtained from such melts at high temperatures. A noncubic crystalline phase that may be Pb3Bi2Ge3O12 is also reported.
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