Crystallization of Anatase TiO2 in Niobium Potassium Phosphate Glasses

Abstract

In this work, the glass forming ability was studied in potassium phosphate glasses with increasing amounts of TiO 2 in order to obtain a glass-ceramic with photocatalytic properties. The first studied series has been the binary system (100-x) KPO 3 -xTiO 2 . Homogeneous and transparent glasses could be obtained with x varying from 10 to 30 mole%. Since the photocatalytic anatase phase could not be precipitated in this system, the ternary system KPO 3 -TiO 2 -Nb 2 O 5 was investigated in order to incorporate higher TiO 2 contents without spontaneous crystallization under cooling. Thermal properties of all glass samples were investigated by DSC and allowed identifying an increase of glass transition temperatures with increasing TiO 2 . For all compositions, exothermic events related with crystallization were also observed and suitable heat-treatments resulted in specific crystalline phases identified by X-ray diffraction. Selective precipitation of the anatase titanium oxide was successfully obtained from the glass compostion 35KPO 3 -25Nb 2 O 5 -40TiO 2 (KN25T40) after heat treatment at 720°C for 2 h, suggesting the possibility of obtaining a glass-ceramic for photocatalytic applications. Structural investigations by Raman were also performed on glasses and glass-ceramics and allowed to point out the glass intermediary behavior of TiO 2 in the phosphate vitreous network where TiO 4 and TiO 6 octahedra are inserted inside the phosphate network with TiO 6 clusters identified at higher TiO 2 contents. Raman analysis also identified anatase TiO 2 in the KN25T40 glass-ceramic.

Transparent glass and glass‐ceramic in the binary system NaPO3‐Ta2O5

“…In fact, nanocrystalline glass-ceramics containing high transition metal oxide content usually exhibit low phonon energies in relation to the glass precursor and are very promising candidates for photonic applications. 7,23 In addition, two well-defined crystallization events at 974°C and 1038°C were observed in this sample, suggesting the occurrence of phase separation under heating. A detailed crystallization study was performed for this composition aiming to obtain nanometric crystallization of the first crystalline phase.…”

“…Based on these results, 50Ta sample has been considered promising for synthesis of transparent glass‐ceramic containing tantalum oxide‐rich crystalline phase. In fact, nanocrystalline glass‐ceramics containing high transition metal oxide content usually exhibit low phonon energies in relation to the glass precursor and are very promising candidates for photonic applications . In addition, two well‐defined crystallization events at 974°C and 1038°C were observed in this sample, suggesting the occurrence of phase separation under heating.…”

“…Recently, structural changes in phosphate glasses has been reported by the addition of WO 3 , Ta 2 O 5 , V 2 O 5 , TiO 2 , and Nb 2 O 5 . In fact, transition metal containing oxide glasses exhibit improved optical properties for photonic applications when compared with pure oxide glass formers .…”

“…11,12 RE-doped glasses are attractive for optical applications such as lasers 13 and telecommunications devices. 14,15 Recently, structural changes in phosphate glasses has been reported by the addition of WO 3 , 16,17 Ta 2 O 5 , 18,19 V 2 O 5 , 20 TiO 2 , [21][22][23] and Nb 2 O 5 1,5,24 . In fact, transition metal containing oxide glasses exhibit improved optical properties for photonic applications when compared with pure oxide glass formers.…”

Structural and optical characterization of crystals obtained via solid state reactions in the In2O3–TiO2–Al2O3 pseudoternary system

“…Three types of crystalline polymorph phases are possible to obtain for TiO 2 : anatase, rutile, and brookite [5]. Properties and characteristics can be varied between these phases such as photoactivity [5,6], phase stability [6], strong oxidizing power of the photogenerated holes, chemical inertness, non-toxicity [2], low cost, band gap of 3.2 eV [7], which in turn make it a very interesting material.…”