The structure of glasses in the TeO2-P2O5 system

The co-effects of two glass-formers in the TeO₂-P₂O₅ system are studied on the basis of neutron diffraction data. The curves for the radial distribution function (RDF) obtained show a high extent of destruction of the short-range order in the tellurite matrix, while the basic co-ordination PO₄ polyhedron remains unchanged. The co-ordination number (cn) of the Te atom changes from 4 to 3+1 and marked tendency towards elongation of the Te-O distances over 2.3 Å is observed. The considerably higher stability of the PO₄ polyhedra and their strong influence on the TeO₄ polyhedra is established. The observed smearing effect of the Te-Te, Te-second O and O-second O distances in the range of 3.8 to 3.9 Å in other tellurite glasses is also characteristic of this system. A structural interpretation of the liquid-liquid immiscibility on the short-range order level in the system is given. A critical composition with 26±5% of the second glass-former is established, above which concentration a stable immiscibility in the tellurite systems is observed. An attempt is made to construct two adequate structural models (microhomogeneous and microheterogeneous) for the short-range order in the glasses studied.     

Optical absorption studies for TeO2-P2O5 and Bi2O3-TeO2-P2O5 glasses

A range of TeO₂-P₂O₅ and Bi₂O₃-TeO₂-P₂O₅ glass systems were prepared. The optical absorption spectra were measured in the spectral range 300–800 nm and it was found that the fundamental absorption of these glasses is dependent on the glass composition. The optical energy gap of binary glasses increases with increasing TeO₂ content while the addition of Bi₂O₃ to TeO₂-P₂O₅ decreases the optical energy gap. The absorption edges of these glasses arise from direct forbidden transitions and occur at photon energies in the range of 2.17 to 2.97 eV for TeO₂-P₂O₅ glasses and 2.63 to 2.32 eV for Bi₂O₃-TeO₂-P₂O₅ glasses depending on their composition.     

Novel low-temperature synthesis of glasses and glass-ceramics in the B2O3-SiO2-P2O5 system

In recent years considerable progress has been made in electronic packaging substrate technology. The future need of miniaturization of devices to increase the signal processing speed calls for an increase in the device density requiring the substrates to be designed for better thermal, mechanical and electrical efficiency. Fast signal propagation with minimum delay requires the substrate to possess very low dielectric constant. Several glasses and glassceramic materials have been identified over the years which show good promise as candidate substrate materials. Among these, borophosphate and borophosphosilicate glass-ceramics have been recently identified to have the lowest dielectric constant (3.8). Sol-gel processing has been used to synthesize borosilicate, borophosphosilicate and borophosphate glasses and glass-ceramics using inexpensive boron oxide and phosphorus pentoxide precursors. Preliminary results of the processing of these gels and the effect of volatility of boron alkoxide and its modification on the gel structure are described. X-ray diffraction, differential thermal analysis and Fourier transform-infrared spectroscopy have been used to characterize the as-as-prepared and heat-treated gels.     

Conduction mechanism at high electric field and switching phenomena in V2O5-P2O5 and V2O5-P2O5-TeO2 glasses

A previous investigation [1] suggests that the conduction in some vanadate glasses is ohmic up to a field of the order of 10⁵ V cm^–1 with an activation energy range from 0.31 to 0.48 eV depending on composition, but independent of temperature above room temperature. In this work the electrical conductivity of these glasses at high electric field is reported. The results suggest that above a field of 4×10⁵ V cm^–1 conduction becomes non-ohmic, and this is found to be due to lowering the potential barrier to the carrier at high electric field. Memory switching is observed in thin blown film samples of both binary and ternary glass systems, and is associated with field-induced crystallization of a localized region and the formation of a conduction channel in the switched area due to a self-heating effect.     

Compositional dependence of infrared absorption spectra studies for TeO2-P2O5 and TeO2-P2O5-Bi2O3 glasses

The infrared absorption spectra of the vitreous TeO₂-P₂O₅ and Bi₂O₃-TeO₂-P₂O₅ systems are studied in the spectral region of 4000 to 200 cm^–1. Absorption bands in this range are assigned. The midband wavenumber and the absorption intensity for the attributed bands are found to be strongly and systematically dependent on glass composition. Quantitative analysis was also attempted to justify our attribution of the observed bands.     

Novels patterns of hydration and new compounds in the ternary system of CaO-Al2O3-P2O5

 The patterns of hydrating and solidifying with the compositional variation of phosphorus-rich, phosphorus-calcium-rich and aluminum-calcium rich regions in ternary system CaO-Al₂O₃-P₂O₅ has been studied in detail, and two new ternary compounds L and H have been synthesized here. The results indicate that the region of 48–56% P₂O₅ doesn’t present cementitiousness, which contains mainly crystal phases of β-C₂P(2CaO·P₂O₅), α-C₃P(3CaO·P₂O₅) and AlPO₄; the phosphorus-calcium-rich region of 21–35% P₂O₅ exhibits substantial cementitiousness, which contains mainly crystal phase of α-C₃P and certain amount of CA(CaO·Al₂O₃) and new phases L/H; and the aluminum-calcium-rich region of 8–18% P₂O₅ is full of promise for cementitiousness. It contains mainly new crystal phase L and certain amount of α-C₃P and CA. The hydration and solidification mechanisms have been preliminarily analyzed by means of XRD, XPS and DTA. It appears that crystal phase CA might hydrate directly to the stable phase of C₃A·6H₂O in the phosphorus-rich case of 21–35% P₂O₅; new phase H has the behavior of rapid setting; and L, being a dominant phase, can prevent cement pastes from significant strength loss in long curing cycles. Received: 12 March 1998 / Accepted: 29 July 1998     

EPR and magnetic susceptibility studies on V2 O5-P2O5-PbO glasses

EPR and magnetic susceptibility investigations on the glass system with 04+ ion content are explained using a simulation program on the assumption of the superposition of two signals, one with hyperfine structure (hfs) typical for isolated ions and another one consisting of a broad line without hfs characteristic for clustered ions. The hfs is not shown for x<3mol%V₂O₅. The EPR data show the presence of V₄₊ ions in a square-pyramidal co-ordination (C_4V) for 3x20mol%V₂O₅. The progressive disappearance of hfs for high V²O⁵ content (>20 mol %) suggests the increase of the associated ion number coupled by superexchange interactions. This result is consistent with magnetic susceptibility data for >3 mol % where the temperature dependence of magnetic susceptibility is described by the Curie–Weiss type law with a negative paramagnetic Curie temperature. The magnetic susceptibility results allowed the estimation of the V⁴⁺/V⁴⁺ + V⁵⁺ ratio in the sample studied.     

Study of structures and properties of ZnO-Sb2O3-P2O5-Na2O glasses

The influence of ZnO substitution by 0–12 wt.% Na₂O on the properties of ZnO-Sb₂O₃-P₂O₅-Na₂O glasses has been investigated. The structure and properties of the glasses with the composition of (13.86-x)ZnO-57.93Sb₂O₃-28.21P₂O_5?x Na₂O (x = 0–12 wt.%) were characterized by infrared spectra (IR), X-ray diffraction and differential thermal analysis (DTA). The results of IR indicated an increase in the intensity of symmetric vibrations of P-O-P bond, which was confirmed by the improvement of water durability with the increasing amount of Na₂O in the range of 0–10 wt.%. Substitution of 10 wt.% Na₂O led to the weight loss of the glass to 5.93 mg/cm^?2 after immersion in deionized water at 50 °C for 24 h. The results of XRD showed that the ability of crystallization decreased, indicating the good thermal stability of the glass. The glass containing 8 wt.% Na₂O had the best properties in every respect and might be an alternative to lead based glasses for the applications, providing further composition improvement.     

Growth kinetics of spherulitic apatite in some MgO-CaO-SiO2-P2O5 glasses

Crystallization of glasses with compositions (wt%) of 11.2 MgO, 33.3 SiO₂, (55.5–x) CaO, and xP₂O₅ (x=18.3, 16.65, 15.825 and 15.0) resulted in a spherulitic apatite phase with different crystal morphologies. An ellipsoidal morphology was observed for x=18.3, 16.65 and 15.825, and an anomalous morphology was observed for x=15.0. A metastable phase, which was similar in some characteristics to apatite, was also found for x=15.0. The growth kinetics of the spherulitic apatite crystals were investigated to explain the above observations. Both the dendrite arms along the [0001] and [1 1¯20] directions of the apatite crystals showed constant growth rates in each glass. Growth-rate anisotropy was found between these two directions. The ellipsoidal shape of the apatite crystals is explained by this growth-rate anisotropy. The growth rates, and the growth-rate anisotropy, varied with the P₂O₅ content in such a manner that the changes in phase formation behaviour can be explained on the basis of the kinetic results.     

The crystallisation of glasses based on eutectic compositions in the system Li2O-Al2O3-SiO2

Structural transformations have been studied in glasses related in composition to the binary eutectic between lithium metasilicate and -spodumene. Crystallisation processes and changes in microstructure during the controlled heating of the glasses have been followed using X-ray diffraction, electron microscopy, high temperature microscopy, thermal analysis and electron spin resonance spectroscopy.The influence exerted by titanium dioxide on the phase relationships, crystal growth rates and micromorphology of the polycrystalline products of heat-treatment has been investigated and the findings used as a basis for proposals on the rôle of TiO₂ during nucleation and crystal growth.     

The crystallisation of glasses based on the eutectic compositions in the system Li2O-Al2O3-SiO2

A study has been made of the crystallisation of glasses based on the eutectic between lithium metasilicate and-eucryptite and of the rÔle of TiO₂ in promoting fine-grained crystallisation. The hypothesis advanced in part 1 of this work is extended to a semi-quantitative measure of the effect of TiO₂.Characteristics of two metastable phases are described in an appendix.     

SnO-BaO-P2O5系统无铅封接

以SnO-BaO-P2O5三元系统玻璃为研究对象,利用差示量热扫描分析仪、热膨胀仪、拉曼光谱仪,分析了玻璃的结构以及玻璃转变温度和热膨胀系数与玻璃组成的关系.获得了该体系玻璃的形成区域,测得该系统的玻璃转变温度为260～360 ℃和热膨胀系数为12～14×10-6 ℃-1.研究发现,当P2O5=45 mol%不变时,玻璃转变温度随着SnO含量的增加而降低;当BaO=10 mol%不变时,玻璃转变温度随着SnO含量的增加先降低后升高.研究表明,该体系玻璃可以作为低温环保封接玻璃潜在的基质材料.     

SnO—BaO—P2O5系统无铅封接玻璃的结构与性质

以SnO—BaO—P2O5三元系统玻璃为研究对象,利用差示量热扫描分析仪、热膨胀仪、拉曼光谱仪,分析了玻璃的结构以及玻璃转变温度和热膨胀系数与玻璃组成的关系．获得了该体系玻璃的形成区域,测得该系统的玻璃转变温度为260～360℃和热膨胀系数为12～14×10^-6℃．研究发现,当P2O5=45mol％不变时,玻璃转变温度随着SnO含量的增加而降低;当BaO=10mol％不变时,玻璃转变温度随着SnO含量的增加先降低后升高．研究表明,该体系玻璃可以作为低温环保封接玻璃潜在的基质材料．     

ZnO-Al2O3-P2O5玻璃水化过程及机理的研究

研究了不同Al2O3/P2O3摩尔比和热历史的ZnO-Al2O3-P2O5玻璃在不同条件下的水化过程,利用XRD对部分水化过程的水化产物进行了晶相分析,探讨了其水化机理.结果表明:Al2O3/P2Os比的增加及退火均可降低ZnO-Al2O3-P2O5玻璃的水化速率;玻璃的水化累计失重量均与水化时间成线性关系,水失重百分数随着水化温度的提高,呈指数规律增加.研究认为:ZnO-Al2O3-P2O5玻璃的水化过程受表面水化层与内部未水化部分间的界面化学反应控制,水化过程中玻璃网络解体,相继生成了[P2O7]4-和白色不溶性物质Zn2P2O7·3H2O.     

Preparation and characterization of sol–gel derived glasses in the ternary Na2O–Al2O3–P2O5 system

A new sol–gel synthesis route to organic free Na₂O–Al₂O₃–P₂O₅ xerogels was developed. These xerogels contain P₂O₅ up to 67.5 mole % and Al₂O₃ up to 20 mole % and could be melted to homogeneous glasses in air at significantly lower temperatures than those applied using the conventionally melting method. Aluminum isopropoxide dissolved in isopropanol, orthophosphoric acid dissolved in isopropanol and sodium nitrate were used as precursors for Al₂O₃, P₂O₅ and Na₂O respectively. Clear stable alcoholic solutions were prepared in the presence of HNO₃. Addition of HNO₃ in the concentration used, enabled homogeneous mixing of the precursors, controlled over the gelation step and prevented the fast precipitation of the AlPO₄ crystalline phase which breaks down the glass formation ability. The sol–gel route developed was investigated using different analytical tools. Differential thermal analysis (DTA) coupled with thermo-gravimetric (TG) analysis indicated that neither organic residues nor sodium nitrate residues were present in the dried gels after gelation. Fourier transform infrared spectroscopy (FTIR) showed the presence of all characteristic phosphate groups and bonds in the dried gels, especially the P=O and the P–O–P bonds. Solid state ³¹P Magic angle spinning nuclear magnetic resonance (MAS NMR) revealed the formation of Q² chain-like polyphosphates of variable polymerization degrees in the dried gels. Solid state ²⁷Al MAS NMR revealed that octahedrally coordinated Al is the preferred moiety in the dried gels. However, powder X-ray diffraction (XRD) investigation indicated the presence of crystalline Q¹ oligomeric pyrophosphate species in the dried gels. Isotropic chemical shifts belonging to these pyrophosphate species were also recorded in the ³¹P MAS NMR spectra. Characterization of the prepared glasses showed that their properties are in very good agreement with those glasses prepared by the conventionally melting method.     

Phase equilibria and immiscibility in the TeO2-P2O5 system

The phase equilibria and immiscibility of mutual glass formers up to 50 mol% P₂O₅ have been studied. Phase analysis indicates the formation of three new phases — incongruent melting Te₄P₂O₁₃, Te₂P₂O₉, and a supposed metacompound. Electron microscope investigations established stable and metastable phase separation. The immiscibility confines the tendency to glass formation up to 25.8 mol % P₂O₅. A reliable interpretation in relation to the morphology of liquid-liquid immiscibility and crystallization is considered.