Structure and physical properties of sodium antimony germanate glasses
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Structure and physical properties of sodium antimony germanate glasses M. Pal MLS Lab, Indian Association for the Cultivation of Science, Calcutta 700 032, India (Received 10 October 1995; accepted 28 March 1996)
The structure and physical properties of sodium antimony germanate glasses with compositions 10Na2 O 2 x Sb2 O3 2 (90 2 x)GeO2 , x 10–30 mol %, prepared by the melt-quenched route have been studied. It is observed from x-ray diffraction, SEM, density and oxygen molar volume, infrared (IR), differential thermal analysis (DTA), and optical absorption that single phase homogeneous glasses with a random network structure can be obtained in this system. The strength and connectivity of the glass network increase with GeO2 content. The main Ge–O stretching vibration also shifts to higher wavelength side. Two oxidation states of antimony, Sb 31 and Sb 51 , are present, while the so-called “germanate anomaly” is absent in these glasses. This study discusses the probable structural reasons behind this type of behavior of these glasses.
I. INTRODUCTION
Germanate glasses are superior to silicate glasses for optical transmission application due to their long IR cutoff wavelength.1 Also, Ge–O has lower bond strength than Si–O, the field strength of Si41 is 2268 nm22 , while that for Ge41 is 1424 nm22 . Binary germanate glasses containing alkali2–4 and alkaline earth materials5–7 have been studied extensively. It is found that small amounts of Sb2 O3 (,10 mol %) favor the network retention in the Ge–O–Ge glasses, while larger amounts caused extensive depolymerization.8 Alkali-germanate glasses containing glass network modifier have been investigated by some workers.9,10 In alkali germanate glasses a socalled “germanate anomaly”, that is, a maximum or minimum of some physical properties (viz. density, refractive index, molar volume, Tg , etc.), was observed. The anomaly has been attributed to the change of coordination number of Ge from four to six.4,5 For some ternary system it is found that Tg can both increase or decrease with the increase of GeO2 .11 It was reported that in hexagonal and vitreous GeO2 , in which the coordinations number of Ge41 is four, the main absorption band appears at ,878 cm21 , whereas in tetragonal GeO2 , where Ge41 has coordination number six, the band occurs at ,688 cm21 .12 Glasses containing transition metal ions have received major attention due to possible applications in electrical threshold, memory switching, and optical switching devices.12,13 These glasses are semiconducting. Semiconduction arises from the hopping of polarons between two valence states of the transition metal ions.14,15 Antimony also behaves like containing Sb2 O3 .16,17 However, detailed studies on the structural and physical properties of the ternary sodium antimony germanate glass system have not been reported yet to our knowledge. J. Mater. Res., Vol. 11, No. 7, Jul 1996
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The purpose of the present work is to
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