Physical Properties of Quenched Glasses in the Li2O-ZrO2-SiO2 System

The behavior and some physical and thermal properties of a 30Li₂O-70SiO₂ base glass composition with addition of ZrSiO₄ in the as-quenched state was investigated with the aid of X-ray diffraction (XRD), differential thermal analysis (DTA), thermal expansion and microhardness measurements, as well as density measurements. Transparent glasses prepared by the addition of ZrSiO₄ up to 10.30 mol% were obtained. ZrSiO₄ was found to decrease the expansion coefficient of the investigated glasses from 11.0 × 10⁻⁶ to 7.96 × 10⁻⁶°C⁻¹. The glass transition and softening point temperatures of the glasses showed a reverse behavior. On the other hand, both hardness and density increased for successive increases of the ZrSiO₄ amounts, with the highest values of 6.3 GPa and 2.65 g/cm³, respectively.     

Infrared Spectra of Rapidly Quenched Glasses in the Systems Li2O-RO-Nb2O5 (R=Ba, Ca, Mg)

Twin-roller quenching produced wide ranges of glass formation in the systems Li₂O-RO-Nb₂O₅ (R=Ba,Ca,Mg). The glass-forming ability is improved with an increase in the ionic radius of R²⁺ ions. The crystallization temperature is increased as Li₂O is replaced by RO or the ionic radius of R²⁺ ions is increased. Infrared spectra revealed that the glass LiNbO₃ (=50Li₂O-0Nb₂O₅) was composed of six-coordinated NbO₆ octahedra, which were joined together by corner-sharing only. In the Li₂O-RO-Nb₂O₅ glasses there exist edge-shared as well as corner-shared NbO₆ octahedra. The edge-shared NbO₆ octahedra in the glasses are increased with an increase in the content of RO or Nb₂O₅, and also with an increase in the ionic radius of R²⁺ ions.     

Preparation and Properties of Nitrogen-Containing Na2O-B2O3 Glasses

Up to 3.3 wt% nitrogen can be incorporated into Na₂O-B₂O₃ glass melts. The melting procedure is described, and structure models are given. In contrast to N-containing silicate glasses, the borate glasses were transparent; however, micrographs of their fracture surfaces showed some crystallinity. Properties were determined as a function of the N and Na₂O contents of the glasses. Compared with N-containing silicate glasses, the properties of borate glasses are much less changed by the nitrogen introduced.     

Elastic Properties of 0.98Li2O-1.0Al2O3-nSiO2 Glasses and Keatite-Phase Glass-Ceramics

Bulk physical properties such as elastic moduli, thermal expansions, and moduli of rupture were measured for a series of 0.98Li₂O-1.0ALO₃- n SiO₂ glasses and the corresponding keatite solid-solution-phase glass-ceramics. The SiO₂ content ranged from n =4 to 12. The magnitude of the elastic properties of the glasses changed monotonically with increasing SiO₂ content. The properties of keatite-phase glass-ceramics depended almost linearly on SiO₂ content, but their behavior differed qualitatively from that of the glasses.     

Microwave Dielectric Properties of 5Li2O–0.583Nb2O5–3.248TiO2 Ceramics with V2O5

The effects of V₂O₅ addition on the sintering behavior, microstructure, and the microwave dielectric properties of 5Li₂O–0.583Nb₂O₅–3.248TiO₂ (LNT) ceramics have been investigated. With addition of low-level doping of V₂O₅ (≤2 wt%), the sintering temperature of the LNT ceramics could be lowered down to around 920°C due to the liquid phase effect. A secondary phase was observed at the level of 2 wt% V₂O₅ addition. The addition of V₂O₅ does not induce much degradation in the microwave dielectric properties but lowers the τ_f value to near zero. Typically, the excellent microwave dielectric properties of ɛ_r=21.5, Q × f =32 938 GHz, and τ_f=6.1 ppm/°C could be obtained for the 1 wt% V₂O₅-doped sample sintered at 920°C, which is promising for application of the multilayer microwave devices using Ag as an internal electrode.     

High-Quartz Solid Solution Phases from Thermally Crystallized Glasses of Compositions Li2O2,MgO).Al2O3,nSiO2

Thermally crystallized glasses of compositions (Li₂,O₂, MgO).Al₂O₃.nSiO₂ were studied by X-ray powder diffraction methods. High-quartz solid solution phases developed at relatively low temperatures and, for n 3.5, transformed at higher temperatures to keatite solid solution phases. Associated phases, if present, were Mg spinel and/or cordierite, or a few other trace phases. The a crystallographic axis (a₀) of high-quartz solid solutions decreased with increase of MgO and/or SiO₂. The c crystallographic axis (c₀) decreased with increasing MgO; it also decreased with increasing SiO₂, but only when MgO content was low. X-ray diffraction photographs of single crystals of high-quartz solid solutions of compositions LiaO.Al₂O₃.nSiO₃ demonstrated that the maintenance of a basic high-quartz structure is the basis of the solid solution relation. Three modifications of the high-quartz structure were recognized in the Li₂O-Al₂O₃−SiO₃ system. These modifications were based on the occurrence and positions of superlattice reflections. The high-quartz solid solution from Li₂O Al₂O₃−2SiO₂, showing streaky reflections in its precession photographs, suggested a defective structure. The term "high-quartz solid solution," with or without additional prefixes specifying the compositional series and modification, was considered the preferred nomenclature for these solid solution phases.     

Kinetics of Crystallization in Li2O-SiO2 Glasses

The kinetics of crystallization of Li₂Si₂O₅ from glasses in the Li₂O-SiO₂ system were studied using quantitative X-ray diffraction. Analysis of the data using the Johnson-Mehl-Avrami equation showed that crystallization occurred through the nucleation and growth of rods. The spherulitic nature of the crystals was substantiated by petrographic examinations of the partially crystalline glass. Analysis of the temperature dependence of the crystallization rate using a modification of the Johnson-Mehl-Avrami equation showed that the activation energy for nucleation was a function of composition and thermal treatment.     

Influence of V2O5 Additions to 5Li2O–1Nb2O5–5TiO2 Ceramics on Sintering Temperature and Microwave Dielectric Properties

The effects of the addition of V₂O₅ on the sintering behavior, microstructure, and microwave dielectric properties of 5Li₂O–1Nb₂O₅–5TiO₂ (LNT) ceramics have been investigated. With low-level doping of V₂O₅ (≤3 wt%), the microstructure of the LNT ceramic changed from a special two-level intergrowth structure into a two-phase composite structure with separate grains. And the sintering temperature of the LNT ceramics could be lowered to around 900°C by adding a small amount of V₂O₅ without much degradation in microwave dielectric properties. Typically, better microwave dielectric properties of ɛ_r=41.7, Q × f =7820 GHz, and τ _f =45 ppm/°C could be obtained for the 1 wt% V₂O₅-doped ceramics sintered at 900°C.     

The Influence of Sb2O3 Addition on the Properties of Low-melting ZnO–P2O5 Glasses

The influence of 0–16 mol% Sb₂O₃ substitution for P₂O₅ on the properties of ZnO–P₂O₅ glasses has been investigated. It was shown that Sb₂O₃ could participate in the glass network and thermal stability of the glasses decreased with increasing Sb₂O₃ content. Glass transition temperature T _g, softening temperature T _s, and water durability all decreased firstly (up to 6 mol% Sb₂O₃ added) and then increased. Substitution of 12 mol% Sb₂O₃ led to a 16°C decrease in T _g and 30°C decrease in T _s, and weight loss of the glass was only 0.42 mg/cm², which is ∼11 times lower than that of the glass without Sb₂O₃ after immersion in deionized water at 90°C for 1 day. The glass containing 12 mol% Sb₂O₃ might be a substitute for Pb-based glasses in some applications.     

Electrical Resistivity Surface for FeO-Fe2O3-P2O5 Glasses

The dc electrical properties and microstructure of x (FeO-Fe₂O₃)-(100 – x )P₂O₅ glasses were investigated up to a maximum of x = 75 mol%. Results indicate that, in general, the minimum resistivity of the glass does not occur at equal Fe^2+] and Fe^3+] concentrations, although for the special case where x = 55 mol% the minimum does occur at Fe^2+]/Fe total = 0.5, as reported by other investigators. Evidence presented shows that the position of the minimum resistivity is a function of total iron content. The minimum shifts to glasses richer in Fe^2+] at higher total iron concentrations.     

Direct Observation of the Crystallization of Li2O-Al2O3-SiO2 Glasses Containing TiO2

The nucleation and crystallization of Li₂O-Al₂O₃-SiO₂ glasses containing TiO₂ were investigated using transmission electron microscopy of thin sections produced from bulk samples. Phase separation occurs during cooling from the melt, and on heating, a large number of titanium-aluminum crystals approximately 50 A in diameter are formed. These crystals are the heterogeneous nuclei for the crystallization of the remaining glass. Photomicrographs of various stages of crystallization show the development of the fine-grained glass-ceramic.     

Semiconductor Passivation and Insulation Properties for Hydroxyl- and Fluoride-Free ZnO-SiO2-B2O3-Al2O3 Glasses Stabilized by Increased P2O5

F⁻- and OH⁻-free ZnO-B₂O₃-SiO₂-Al₂O₃-P₂O₅ glasses used for semiconductor-device passivation or insulation are investigated with regard to compositional dependencies for thermal expansion, viscosity points, and metal oxide semiconductor (MOS) capacitor properties. The experimental data show that thermal expansion increases, and flow points decrease, when P₂O₅ is substituted for B₂O₃. MOS capacitors passivated by OH⁻- and F⁻-free ZnO-based glasses exhibit normal capacitance-voltage curves.     

Sintering, Crystallization, and Properties of B2O3/P2O5-Doped Li2O·Al2O3·4SiO2 Glass-Ceramics

Sintering, crystallization, microstructure, and thermal expansion of Li₂O·Al₂O₃·4SiO₂ glass-ceramics doped with B₂O₃, P₂O₅, or (B₂O₃+ P₂O₅) have been investigated. On heating the glass powder compacts, the glassy phase first crystallized into high-quartz s.s., which transformed into β-spodumene after the crystallization process was essentially complete. The effects of dopants on the crystallization of glass to high-quartz s.s. and the subsequent transformation of high-quartz s.s. to β-spodumene were discussed. The major densification occurred only in the early stage of sintering time due to the rapid crystallization. All dopants were found to promote the densification of the glass powders. The effect of doping on the densification can fairly well be explained by the crystallization tendency. All samples heated to 950°C exhibited a negative coefficient of thermal expansion ranging from about −4.7 × 10^-6 to −0.1 × 10^-6 K^-1. Codoping of B₂O₃ and P₂O₅ resulted in the highest densification and an extremely low coefficient of thermal expansion.     

Phase Diagram for a Portion of the System Li2O-Nd2O3-P2O5

In the ternary system Li₂O-Nd₂O₃-P₂0₅, part of the phase diagram relevant to the growth of single LindP₄O₁₂ (LNP) crystals was examined. LNP melts incongruently and decomposes into NdP₃O₉ and liquid at the peritectic temperature of 970°C. For the crystal growth, an Li₂O-P₂O₅ mixture should be used as a flux. The melt compositions from which LNP nucleates were clarified.     

Tungsten Bronze Field and Melt Growth of Crystals in the Na2O-BaO-Nb2O5 System

The extents of the liquidus and solidus fields were determined for tungsten bronze-type solid solutions in the Na₂O-BaO-Nb₂O₅ system by DTA and melt crystal growth experiments. Bronze-type solid solutions exist to 7.1Na₂O-34.9BaO-58Nb₂O₅ in the Nb₂O₅-rich region and from 12Na₂O-38BaO-50Nb₂O₅ to 4.6Na₂O-45.4BaO-50Nb₂O₅ along the NaNbO₂-BaNb₂O₆ join, which includes NaBa₂Nb₅O₁₅=10Na₂O-40BaO-50Nb₂O₆. There is little, if any, solid solubility of compositions with a deficiency of Nb₂O₅. Curie temperatures decline rapidly and dielectric constant peaks broaden with Nb₂O₅ substitution because the Nb:O ratio becomes greater than the octahedral 1:3 ratio. Useful ferroelectrics exist along the NaNbO₃-BaNb₂O₆ join where the Nb:O ratio is 1:3. Large striae-free crystals, with less optical scattering than Czochralski-grown crystals, were grown from unseeded Na₂O-rich melts (e.g. 15Na₂O-37.5BaO-47.5Nb₂O₅) cooled from 1520° to 1300°C at 2°C/h. Annealing effects on these crystals whose compositions lie on the NaNbO₃-BaNb₂O₆ join are discussed.     

Transformation-Range Behavior of Li2O-(Al, Ga)2O3-SiO2 Glasses

The transformation-range viscosity and the glass transformation temperatures were measured for three series of Li₂O-R₂O₃-SiO₂ glasses containing varying alumina-to-gallia ratios. The results indicate that these properties vary linearly with the alumina/gallia ratio. These results suggest that these glasses are isostructural and that no "mixed intermediate oxide" effect occurs.     

Free Volume of Network-Forming Oxide Glasses in the Systems P2O5-(GeO2,TeO2,Sb2O3,V2O5)

The free-volume fraction (V_f) defined by Simha and Boyer was measured for network-forming oxide glasses in the systems P₂O₅-(GeO₂, TeO₂,Sb₂O₃.V₂O₅). The V_f values varied from 0.06 to 0.25. The systems P₂O₅-TeO₂: and P₂O₅-Sb₂O₃ have V_f∼0.1, which is near the magnitude of the free-volume fraction for normal metaphosphate glasses and many organic high polymers.     

Internal Friction of Network-Forming Oxide Glasses in the System P2O5-(GeO2, TeO2, Sb2O3, V2O5)

The internal friction of only network-forming oxide glasses containing a P₂O₅ component, i.e., in the systems P₂O₅-GeO₂, P₂O₅-TeO₂, P₂O₅-Sb₂O₃, and P₂O₅-V₂O₅, was measured as a function of temperature by a free torsional vibration method. P₂O₅-TeO₂ and P₂O₅-Sb₂O₃ glasses exhibited clearly high-temperature peaks in a plot of internal friction vs temperature in spite of the absence of nonbridging oxygens and network modifiers. Therefore, we conclude that the high-temperature peaks appeared when strong and weak parts coexisted in the network structure.     

Electrical Conductivity of TiO2-V2O5-P205 Glasses

The dc conductivities (σ) of V₂O₅-P₂O₅ glasses containing up to 30 mol% TiO₂ were measured at T=100° to ∼10°C below the glass-transition temperature. Dielectric constants from 30 to 10⁶ Hz, densities, and the fraction of reduced V ion were measured at room temperature. The conduction mechanism was considered to be small polaron hopping between V ions, as previously reported for V₂O₅-P₂O₅ glass. The temperature dependence of σ was exponential with σ = σ₀ exp(-W/kT ) in the high-temperature range. When part of the P₂O₅ was replaced by TiO_2,σ increased and W decreased. The hopping energy depended on the reciprocal dielectric constant which, in this case, increased with increasing TiO₂ content.