Potassium niobium silicate (KNS) glasses the composition of which is characterized by the K2O/Nb2O5 molar ratio ranging from 0.85 to 1.2 and SiO2 50-54 mol% were examined in order to clarify the influence of chemical composition on formation of transparent nanostructured state of glasses. Differential thermal analysis, X-ray diffraction and scanning electron microscopy were used to study the non-isothermal crystallization of the KNS glasses as well as their morphological features. It was found that all glasses devitrify in three steps forming unidentified phases at the first two ones while at higher temperature (1000-1100 degreesC) the crystallization of K3Nb3O6Si2O7 takes place. For prolonged heat treatment time (more than 5 h) at high temperature (1050-1100 degreesC) the transformation of this phase into the KNbSi2O7 ferroelectric one occurs in some extent. Nanostructuring occurs at the first stage of the devitrification process. It results from two partially overlapped processes: amorphous phase separation and subsequent crystallization. It was shown that only for the glass with the K2O/Nb2O5 molar ratio equal to 0.85 and SiO2 50 mol% it is possible to separate the above processes by isothermal heat treatments at 680 degreesC obtaining fully transparent nanostructured samples. These samples contain nanocrystals 10 times smaller than the amorphous inhomogeneities of the phase separated matrix in which are dispersed. (C) 2004 Elsevier B.V. All rights reserved.
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机译：考察了组成为K2O / Nb2O5摩尔比为0.85至1.2和SiO2 50-54 mol％的特征的硅酸铌铌（KNS）玻璃，以阐明化学成分对形成透明纳米结构态的影响。眼镜。用差示热分析，X射线衍射和扫描电子显微镜研究了KNS玻璃的非等温结晶及其形态特征。发现所有玻璃在前两个阶段中分三步失透，形成未确定的相，而在更高的温度（1000-1100℃）下发生K 3 Nb 3 O 6 Si 2 O 7的结晶。在高温（1050-1100摄氏度）下，延长的热处理时间（超过5小时）在某种程度上会发生此相向KNbSi2O7铁电体的转变。纳米结构发生在失透过程的第一阶段。它来自两个部分重叠的过程：非晶相分离和随后的结晶。结果表明，仅对于K 2 O / Nb 2 O 5摩尔比等于0.85且SiO 2为50摩尔％的玻璃，可以通过在680℃下进行等温热处理来分离上述工艺，从而获得完全透明的纳米结构样品。这些样品包含的纳米晶体比分散在其中的相分离基质的非晶态不均匀性小10倍。 （C）2004 Elsevier B.V.保留所有权利。
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