Crystallization of fluorozirconate glasses

The crystallization of a number of glasses of the fluorozirconate family has been studied using powder X-ray diffraction and differential scanning calorimetry, as a function of time and temperature of heating. The main crystalline phases were β-BaZrF₆ and β-BaZr₂F₁₀. Stable and metastable transformations to the low temperature α phases were also investigated. The size of crystallites in fully devitrified glasses was calculated to be $\text{～ 600}\text{A}\text{?}$ from line broadening of the X-ray diffraction peaks.     

The electrical conductivity of fluorozirconate and chloro-fluorozirconate glasses

The electrical conductivities of glasses in the ZrF₄-BaF₂ and ZrF₄-BaF₂-BaCl₂ systems have been measured as a function of temperature. The conductivies of binary fluorozirconate glasses had values comparable to those previously measured for ternary systems. The introduction of chlorine in the glass network markedly decreased the electrical conductivity and increased the activation energy for conduction. The decrease in conductivity could not be explained exclusively on the basis of zero mobility for the Cl atoms; it is proposed that these atoms effectively hinder the motion of the conducting fluorine ions. The activation energy for electrical conduction in fluorozirconate glasses was analysed via a modification of the Anderson and Stuart model for anionically conducting glasses, in which the electrostatic energy was found to predominate. In chlorofluorozirconate glasses, this term appears to be less predominant.     

Preparation and properties of fluorozirconate glasses containing divalent europium

The glass forming region of the (ZrF₄BaF₂ThF₄)EuF₂ system has been studied. EuF₂ was found to replace up to about 85% of the BaF₂ in a glass with a composition .615 ZrF₄, .32BaF₂, .07ThF₄. The glass transition temperature is seen to increase with the EuF₂ concentration. The 4f⁷→ 4f⁶5d¹ transition of the Eu⁺² ion in the glass matrix was studied by optical absorption and compared with data taken on crystalline compounds containing Eu⁺² in different environments. It is concluded from these results that the Eu⁺² ion - and also the Ba⁺² ion - is coordinated by 12 fluorides in the glass.     

Fluoride bridging modes in fluorozirconate glasses by x-ray and computer simulation studies

A second characteristic ZrZr distance due to edge-sharing (ZrF_n) polyhedra which is observed in crystalline α-ZrF₄ (high temperature form) and is also suggested by recent X-ray studies of BaF₂ZrF₄ glasses, has been observed in ion dynamics computer simulation studies. Experimental X-ray and computer simulation results both imply that about one out of each four bridges between Zr pairs involve two fluoride ions, and that this proportion is almost independent of composition in the binary system.     

Influence of processing conditions on IR edge absorption in fluorohafnate and fluorozirconate glasses

The influence of processing conditions on the IR absorption edge of fluoride glasses with the composition 62 MF4 1b 33 BaF₂ 1b 5 LaF₃ (M = Hf or Zr) is reported. At higher values of the absorption coefficient (α > 1 cm^?1), the IR edge is nearly independent of processing conditions and appears to be intrinsic. At lower values (α < 1cm^?1) extrinsic features attributed to oxide impurities appear; these are suppressed when glass melting is carried out in a reactive atmosphere of CCl₄. Comparison of our results for HfF₄- and ZrF₄ based glasses shows that substitution of HfF₄ for ZrF₄ shifts the IR edge to longer wavelengths, but the intrinsic absorption curves are nearly parallel over the frequency range investigated.     

The effect of nitrogen addition on certain properties and structure of fluorozirconate glasses

The effect of nitrogen on the properties and structure of fluorozirconate glasses in the system ZrF₄-BaF₂-LaF₃-AlF₃ (ZBLA) was investigated. Nitrogen was introduced by means of aluminium nitride. The substitution of fluorine by nitrogen in ZBLA glasses resulted in a considerable increase of microhardness, reduction of the linear expansion coefficient, and a small increase in characteristic temperatures. Structural investigations comprised RDF and Fourier transform-infrared (FT-IR) examinations. From radial distribution function (RDF) it followed that the introduction of nitrogen caused an increase of the mean distances Zr-F(N), Ba-F(N), La-F(N). From FT-IR spectra, it followed that nitrogen became incorporated into the bridging fluorine atoms which was evinced by a shifting of bands deriving from the bending vibrations between the [ZrF₆]^2– octahedra towards higher wave numbers.     

Influence of alkali content and alkali mixing on the chemical durability of fluorozirconate glasses

The corrosion of alkali-containing fluorozirconate glasses in water and acidic and alkaline solutions was studied with glasses of the compositions (100–x) (0.6ZrF₄·0.1AlF₃·0.3BaF₂)· xLiF and 48ZrF₄·8AlF₃·24BaF₂·xLiF·(20–x)NaF. The corrosion of the glasses in deionized water and 0.1 n HCl solution is mainly controlled by diffusion with an inductive period due to the passage from reaction-controlled to diffusion-controlled mechanisms, and the weight loss of glass increases with increasing LiF content in the single-alkali glasses. There was no appreciable effect of alkali mixing on the corrosion of glasses in deionized water and 0.1 n HCl solution. The glasses exhibited good stability in alkaline solution. The weight loss due to corrosion of the glasses in acidic buffered solution increased exponentially with increasing LiF content.     

Effect of oxide dopant on the structure of fluorozirconate glasses studied by X-ray photoelectron spectroscopy

The effect of oxide dopant on the structure of 62ZrF₄-30BaF₂-8LaF₃ (mol%) glass by equimolar substitution of BaO for BaF₂ was studied by X-ray photoelectron spectroscopy (XPS). The XPS spectra of La 3d, Ba 3d, F 1s, O 1s and Zr 3d were measured. From the deconvoluted results for the XPS spectra of elements in the glass, it was proposed that the oxide ions added to the glass mainly bond to Zr⁴⁺ and replace the bridging fluoride ions resulting in the formation of the F-Zr-O bond. Further analyses indicated that the oxide ions mainly play a non-bridging role instead of a bridging role in the glass structure.     

Direct current electrical conduction in lead tungsten phosphate glasses

Measurements have been made on d.c. electrical conductivity of semiconducting lead tungsten phosphate glasses (X mol% WO₃–(60–x) mol% PbO–40 mol% P₂O₅;x= 10, 20, 30, 40, 50 and 60) of six different compositions over a temperature range of 240 to 500 K. It is shown that the conduction can be described by a small polaron hopping model. When the WO₃ content is 30 mol% the d.c. conductivity _dc decreases and the activation energyW increases with increasing WO₃ content and the glass samples exhibit predominant ionic conduction, however, when the WO₃ content is > 30 mol%, _dc increases andW decreases with the increase of tungsten ion concentration and the glass samples exhibit electronic conduction. The electronic conduction in these glasses havingx > 30 mol% seems to be adiabatic. Greaves variable range hopping has been found to be valid. The value of the electron wavefunction decay constant a is of the order of 16 nm^–1. A minimum in the d.c. conductivity has been observed when the PbO concentration is 30 mol%.     

Fast Li+ conduction in fluoroborate glasses

Following recent measurements of very high d.c. conductivities in complex Li fluoride-borate-sulfate glasses, we have performed systematic measurements in the Li₂OLiFB₂O₃ system. All glasses studied have essentially the same Arrhenius pre-exponential constant. Converting the data to conductivity relaxation times the pre-exponential constant corresponds to a frequency considerably higher than the Li⁺ - cage “rattling” frequency. Connections between the a.c. conductivity and the IR absorptivity are discussed.     

Electrical conduction in copper phosphate glasses containing nickel or cobalt

A variation in d.c. conductivity and activation energy of 35 mol%CuO-65mol%P₂O₅ glasses is observed as CuO is gradually replaced by NiO or CoO. These results are believed to be due to the change in the redox ratio of the two transition metal oxide glasses, which causes an increase and then a decrease of polaron hopping transitions between the ions of the same element and between the ions of the different transition metal elements.     

Glass formation region and lithium ion conduction in the oxyfluorophosphate glasses

Oxyfluorophosphate glasses containing about 80 mol% of [LiF+Li₂O] show unusually high lithium ion conductivity at elevated temperatures. A detailed investigation has been carried out on the glasses prepared by both conventional cooling and a rapid quenching technique. Chemical analysis of the glasses reveals fluorine loss during melting and it becomes difficult to make glasses with exact predetermined compositions. Electrical conductivity of the glasses, determined from complex impedance analysis increases with Li₂O content. A glass with nominal composition 70 LiF15 Li₂O15 Al(PO₃)₃ shows the highest conductivity (~ 1.3×10^–3 ohm^–1 cm^–1 around 200° C) among all the compositions studied. An interesting feature of the impedance plot is the near perfect semicircle for bulk relaxation indicating a narrow distribution of relaxation times. This has been explained on the basis of a relatively small proportion of lithium ions which are mobile. The electrical conductivity of the glasses is found to be essentailly independent of dissolved water content. The infrared spectra of these glasses (2 to 50m region) could not produce much useful structural information.     

Direct and alternating electrical conduction in copper phosphate glasses containing praseodymium and calcium

Glasses of various compositions were prepared and included Pr₆O₁₁-CuO-P₂O₅ and Pr₆O₁₁-CaO-CuO-P₂O₅. The direct electrical conduction mechanism was generally discussed in terms of small polarons for the whole series of glasses. Alternating electrical conduction was discussed according to the Elliott model and the Meyer-Neldel rule.     

Chemical approach to the conduction mechanism in copper tellurite glasses containing lutetium oxide

Measurements of d.c. electrical conductivity were made on 65TeO₂-(35 -x)CuO-xLu₂O₃ (mol%) glasses with x=0, 1, 2, 3, 4. The experimental results show that whenx is changed from 1 to 2 mol%, the conductivity increases due to the additional electrons obtained by the oxidation of TeO₂ as well as due to the Cu⁺ Cu²⁺ transition under the effect of interelectronic repulsion in the 4f shell of the lutetium present in the glass. Whenx is increased to greater than 2 mol%, the conductivity decreases because hopping is inhibited due to the formation of oxygen bridge associates or because of the strong ligand repulsive field of lutetium indicating its non-reactivity in the glassy network. The conductivity has a distinct maximum atx=2.     

Correlation of electrical properties and internal friction in mixed conduction glasses containing ionic and electronic conduction (1) Fe2O3-Na2O-P2O5 glasses

The electrical properties and internal friction in (40–x)Fe₂O₃·xNa₂0.60P₂O₅ glasses were measured. Two or three peak on internal friction were observed in the temperature range of –100 to 300° C at a frequency of about 1 Hz. The peak area of internal friction could be explained quantitatively by the additivity law of diffusion of Na⁺ ion and hopping of electrons which are carriers similar to those of dielectric loss. Activation energy, peak temperature of dielectric loss and internal friction showed almost the same value. Both relaxation phenomena have the same mechanism which is due to the diffusion of Na⁺ion and the hopping of electrons between Fe²⁺ Fe³⁺. The high-temperature peak is assumed to result from the interaction between protons or alkali ions and non-bridging oxygen.