Thermal, Structural, and Crystallization Properties of New Tantalum Alkali‐Germanate Glasses

Abstract

In this work, new glass compositions were prepared in the ternary system GeO 2 -K 2 O-Ta 2 O 5 . Potassium oxide was added to reach the complete melt of the starting mixture and two composition series were investigated: the first one with a constant K 2 O molar content of 10% in the ternary system (90-x) GeO 2 -10K 2 O-xTa 2 O 5 and the second one with the same molar content of K 2 O and Ta 2 O 5 in the ternary system (100-2x)GeO 2 -xK 2 O-xTa 2 O 5 . Homogeneous and transparent glasses could be obtained between x = 0 and 20. X-ray diffraction analyzes of samples with x = 25 identified orthorhombic Ta 2 O 5 in the first series and an isostructure of K 3.8 Ge 3 Nb 5 O 20.4 in the second series where it is assumed that Ta 5+ ions are inserted in the Nb 5+ sites. As one of our goal with these materials is related with the preparation of glass-ceramics containing Ta 2 O 5 nanocrystals, the first series has been selected for further characterizations. An increase in glass-transition temperatures with increasing Ta 2 O 5 content as well as an increase of the thermal stability from x = 0 to 10 has been identified by differential scanning calorimetry. For higher contents, crystallization events were identified. Fourier transform infrared and Raman spectroscopic characterizations allowed to point out the intermediary behavior of Ta 2 O 5 in the vitreous network where TaO 6 octahedra are inserted inside the germanate network with TaO 6 clusters identified at higher Ta 2 O 5 contents. Heat-treated samples with high tantalum contents (x = 15 and 20) exhibit preferential precipitation of orthorhombic Ta 2 O 5 with nanometric size, suggesting the possibility of obtaining transparent glassceramics for optical applications.

High niobium oxide content in germanate glasses: Thermal, structural, and optical properties

“…The thermal stability further decreases for higher Nb 2 O 5 concentrations. From this content, as previously studied in tantalum germanate glasses, the Nb 2 O 5 solubility in the germanate liquid reaches a limit and a large amount of niobium oxide progressively forms Nb 2 O 5 ‐rich regions with NbO x clusters which behave as nuclei favoring crystallization . For this reason also a more pronounced crystallization peak can be observed for samples 15Nb and 20Nb.…”

“…In addition, glasses containing transition‐metal oxides in the amorphous network are interesting for their ability to produce nanocrystalline transparent glass‐ceramics after suitable heat treatments . Recently, structural changes due to the addition of Ta 2 O 5 , V 2 O 5 , TiO 2 , WO 3 , Nb 2 O 5 , into germanate glasses has been reported.…”

Design & development of a novel glass polyalkenoate cement for sternal fixation and repair, in the event of median sternotomy surgery

“…The NC of the glass series was calculated using Eq. 3.1 considering the molar compositions of the formulated glasses (Table 3.1) where SiO2 and P2O5 are considered as network formers [286,287], CaO and SrO as network modifiers [287] and Ta2O5 and ZnO as intermediates [280,[288][289][290]. The authors assume the following conditions for the network intermediates: NC 1 : Ta2O5 and ZnO as network formers, NC 2 : Ta2O5 and ZnO as network modifiers, NC 3 : Ta2O5 as a network former and ZnO as a network modifier and NC 4 : Ta2O5 as a network modifier and ZnO as a network former.…”

Constructing Rh–Rh3+ modified Ta2O5@TaON@Ta3N5 with special double n–n mutant heterojunctions for enhanced photocatalytic H2-evolution

“…24 The main peak at 590 cm À1 in Rh-Ta 2 O 5 , which is not observed in the other samples, is related to the bending vibration of TaO 6 octahedral units. 25 For Ta 2 O 5 @ Ta 3 N 5 and Rh-Ta 2 O 5 samples, the peaks at 1600 cm À1 and 1667 cm À1 are attributed to the stretching vibration of C]O adsorbed and chemisorbed on the surface, 26,27 respectively, and the peaks at 1122 cm À1 to the C-O-C symmetric stretching vibration, 28 and the peaks at 1037 cm À1 to the bridged bidentate carbonate, 29 which result from the residual organic groups on the surfaces. In contrast, they are not found in our target materials, indicating that the most surface residues were eliminated by the high temperature nitridation process.…”