Erbium zirconium phosphate Er<Subscript>0.33</Subscript>Zr<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> of the NaZr<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> family. Structure contraction on heating

Erbium zirconium phosphate Er_0.33Zr₂(PO₄)₃, a member of the family of structural analogs of NaZr₂(PO₄)₃ (NZP), was prepared by the sol-gel process and studied by X-ray phase analysis, IR spectroscopy, and differential scanning calorimetry. The behavior of erbium zirconium phosphate on heating in the temperature interval from 25 to 625°C was studied by high-temperature X-ray diffraction. Expansion and contraction along different crystallographic directions and contraction of the structure as a whole were found. The overall contraction is due to higher contribution of the negative axial thermal expansion coefficients α _a and α _b to α_av and hence to the volume expansion of the phosphate. On heating to 900°C, the NZP structure is preserved.     

Fabrication of NaZr<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>-type ceramic materials by spark plasma sintering

Ceramic materials based on Ca_0.5Zr₂(PO₄)₃ and NaFeNb(PO₄)₃, structural analogs of NaZr₂(PO₄)₃ (NZP), were prepared by spark plasma sintering. At sintering temperatures of 1100–1200 and 880°C and sintering times of 12 and 3 min, the relative densities reached were 99.1 and 99.9%, respectively. According to X-ray diffraction data, the sintering process caused no changes in phase composition. The ceramics had a dense, homogeneous microstructure and ranged in grain size from 0.5 to 2.5 μm.     

Superprotonic CsH<Subscript>2</Subscript>PO<Subscript>4</Subscript>-CsHSO<Subscript>4</Subscript> solid solutions

We have performed partial HSO₄⁻ substitution in CsH₂PO₄ and studied the associated structural changes and the proton conductivity of the resultant (CsH₂PO₄)_{1 − x} (CsHSO₄) _x solid solutions in the range x = 0.01–0.3. The results indicate that, at room temperature, the solid solutions are disordered. In the range x = 0.01–0.1, they are isostructural with the low-temperature phase of CsH₂PO₄ (sp. gr. P2₁/m), and their unit-cell parameters increase with x, whereas in the range x = 0.15–0.3 the solid solutions are isostructural with the high-temperature, cubic phase of CsH₂PO₄ (Pm3m), and their unit-cell parameter decreases. The conductivity of the (CsH₂PO₄)_{1 − x} (CsHSO₄) _x solid solutions with x ≤ 0.3 depends significantly on their composition and increases at low temperatures by up to four orders of magnitude, approaching that of the superionic phase of CsH₂PO₄ in the range x = 0.15–0.3 because of the hydrogen bond weakening and increased proton mobility. The conductivity of the superionic phase decreases with increasing x by no more than a factor of 1.5–2, and the superionic phase transition, which occurs at 231°C in CsH₂PO₄, shifts to lower temperatures and disappears for x ≥ 0.15. The activation energy for low-temperature conduction decreases with increasing x: from 0.9 eV in CsH₂PO₄ to 0.48 eV at x = 0.1.     

Crystallographic evaluation of sodium zirconium phosphate as a host structure for immobilization of cesium

Sodium zirconium phosphate (NZP) is a potential material for immobilization of nuclear effluents. The existence of cesium containing NZP structure was determined on the basis of crystal data of solid solution. It was found that up to ~9.0 wt% of cesium could be loaded into NZP formulations without significant changes of the three-dimensional framework structure. The crystal chemistry of Na_1−x Cs _x Zr₂P₃O₁₂ (x = 0.1–0.4) has been investigated using General Structure Analysis System programming. The CsNZP phases crystallize in the space group R-3c and Z = 6. Powder diffraction data have been subjected to Rietveld refinement to arrive at a satisfactory structural convergence of R-factors. The unit cell volume and polyhedral (ZrO₆ and PO₄) distortion increase with rise in the mole% of Cs⁺ in the NZP matrix. The PO₄ stretching and bending vibrations in the infrared region have been assigned. SEM, TEM, and EDAX analysis provide analytical evidence of cesium in the matrix.     

Phase relations in the aluminothermic reduction of ZrO<Subscript>2</Subscript>

This paper presents thermodynamic evaluation of reactions between ZrO₂ and aluminum, which indicates that the aluminothermic reduction of zirconium oxides at temperatures above 600°C is only possible when Al _x Zr _y intermetallic compounds form in the metallic phase. Thermodynamic analysis results are supported by experimental data, which demonstrate that, at ZrO₂: Al ratios in the range 0.4–1.4, the aluminothermic reduction of ZrO₂ leads predominantly to the formation of the congruently melting compounds Al₂Zr and Al₃Zr. The phase formation in the slag yields various forms of calcium aluminates and calcium zirconates and leads to a gradual reduction in the oxidation state of the zirconium.     

Characterization of Ba<Subscript>0.9</Subscript>Sr<Subscript>0.1</Subscript>TiO<Subscript>3</Subscript> prepared by low temperature chloride aqueous synthesis

Ba_0.9Sr_0.1TiO₃ powder was processed at 80°C by reacting Ti sol in aqueous solutions that contained BaCl₂, SrCl₂ and NaOH at atmospheric pressure. Well-crystallized, spherical, nanosizes powders were formed by this method. The powders were found to have a cubic structure, which was retained even after heating at 900°C. Sintering at 1400°C, led to the formation of a tetragonal structure with a secondary phase of Ba₆Ti₁₇O₄₀. Abrupt grain growth was observed at 1400°C. The electrical response of the sample sintered at 1400°C has three electrically different regions. Each region of the sample is represented by different RC element. Element 1 (R ₁ C ₁) is the most resistive and its capacitance ishigh (0.5 nFcm⁻¹) indicating a thin region, probably the grain boundary. Element 2 (R ₂ C ₂) shows a smaller resistance value compared to element 1. The capacitance value of element 2 is temperature-dependent and displays a Curie–Weiss behaviour, indicative of a ferroelectric material above T _c. The lower capacitance of C ₂ (15 pFcm⁻¹) indicates that it is a much thicker region than element 1 and can be assigned as a ferroelectric bulk region. Element 3 is probably an electrode effect.     

Synthesis of Ba<Subscript>3</Subscript>ZnNb<Subscript>2</Subscript>O<Subscript>9</Subscript>−Sr<Subscript>3</Subscript>ZnNb<Subscript>2</Subscript>O<Subscript>9</Subscript> solid solution and their dielectric properties

Oxides of the type, Ba_3-xSr_xZnNb₂O₉ (0 ≤x ≤3), were synthesized by the solid state route. Oxides calcined at 1000°C show single cubic phase for all the compositions. The cubic lattice parameter (a) decreases with increase in Sr concentration from 4.0938(2) forx = 0 to 4.0067(2) forx = 3. Scanning electron micrographs show maximum grain size for thex = 1 composition (∼ 2 μm) at 1200°C. Disks sintered at 1200°C show dielectric constant variation between 28 and 40 (at 500 kHz) for different values of x with the maximum dielectric constant atx = 1.     

Production of opaque frits with low ZrO<Subscript>2</Subscript> and ZnO contents and their industrial uses for fast single-fired wall tile glazes

The amounts of zirconium and zinc oxides, which raise the production costs of ceramic glazes, were decreased in fast single-fired wall tile frit compositions and an industrial frit production was conducted. Opacity of the fired frit-based glazes was accomplished by compositional modifications of frits with no other nucleating agent. It was determined that the ratios of Al₂O₃/ΣR₂O, Al₂O₃/ΣRO, and Al₂O₃/B₂O₃ have significant effects on decreasing ZrO₂ and ZnO levels in the frit composition. A reduction of 25% in both zirconia and zinc oxide contents of frit batches, with respect to the reference frit (R) containing 6–10% ZrO₂ and 6–10% ZnO for a glossy white opaque wall tile glaze, was achieved in the ZD glaze consisting of 4.5–7.5% zirconia and 4.5–7.5% ZnO in its frit composition. It was concluded that zircon was the main crystalline phase of the glaze contributing the opacity. The ZD frit-based glaze has a thermal expansion coefficient value of 61.13 ± 0.32 × 10⁻⁷ °C⁻¹ at 400 °C which well matches to that of the wall tile body. TS EN ISO 10545 standard tests were also applied to the final ZD glaze. It is confirmed that the production cost of a fast single-fired wall tile glaze can be decreased by 15–20% with the successful new frit developed.     

Effect of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> on the properties of nanocrystalline ZrO<Subscript>2</Subscript> + 3 mol % Y<Subscript>2</Subscript>O<Subscript>3</Subscript> powder

We have studied the properties of nanocrystalline ZrO₂〈3 mol % Y₂O₃〉 and 90 wt % ZrO₂〈3 mol % Y₂O₃〉-10 wt % Al₂O₃ powders prepared via hydrothermal treatment of coprecipitated hydroxides at 210°C. The results demonstrate that Al₂O₃ doping raises the phase transition temperatures of the metastable low-temperature ZrO₂ polymorphs and that the structural transformations of the ZrO₂ and Al₂O₃ in the doped material inhibit each other.     

Synthesis and properties of AgTi<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>-based NASICON-type phosphates doped with Nb<Superscript>5+</Superscript>, Zr<Superscript>4+</Superscript>, and Ga<Superscript>3+</Superscript>

We have synthesized materials based on a silver titanium phosphate with partial substitution of tri-, tetra-, or pentavalent cations for titanium: Ag_1±x Ti_2−x M _x (PO₄)₃ (M = Nb⁵⁺, Ga³⁺) and AgTi_2−x Zr _x (PO₄)₃. The materials have been characterized by X-ray diffraction and impedance spectroscopy and have been shown to have small thermal expansion coefficients. Their ionic conductivity has been determined. Silver ions in these materials are difficult to replace with protons.     

ZrO<Subscript>2</Subscript> foams for porous radiant burners

In this work, Y₂O₃-stabilized ZrO₂ (YSZ) foams with low relative density were developed through the replication method, for application as porous radiant burners. The ceramic foams were produced by impregnation of open-cell polyurethane foams with aqueous suspensions and different fractions of raw materials: ZrO₂–8% Y₂O₃ (8YSZ) powder, and additives. The materials were milled for 10–40 min. The impregnated foams were dried and submitted to a heat treatment for polyurethane elimination at 1000 °C for 1 h, with subsequent sintering of the remaining ceramic structure at 1600 °C for 2 h, which resulted in YSZ foams with low relative density (0.07). The structural analysis revealed a cellular structure with an average mechanical strength of 95.6 kPa. The radiation efficiency (>19%) was obtained by tests with different air/fuel ratio. The ceramic matrixes exhibited high performance and structural integrity at high operation temperatures (1400 °C).     

Synthesis,crystal structure,and proton conductivity of KFe(H<Subscript>2</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript>)<Subscript>2</Subscript>

KFe H₂P₂O7)₂ is synthesized at 443 K in molten polyphosphoric acids containing K and Fe ions, and its crystal structure is determined: triclinic unit cell with a = 4.9974(6) Å, b = 7.4766(9) Å, c = 7.8185(9) Å, = 82.29(2)°, = 83.37(2)° , = 74.13(2)° ; Z = 1, sp. gr. P . The structure is made up of infinite ribbons formed by corner-shared PO₄ tetrahedra and FeO₆ octahedra, with the K atoms in between. Neighboring ribbons are linked by hydrogen bonds. The proton conductivity of potassium iron(III) dihydrogen diphosphate is rather low.Translated from Neorganicheskie Materialy, Vol. 41, No. 1, 2005, pp. 74–77. Original Russian Text Copyright © 2005 by Chudinova, Murashova, Ilyukhin, Tarnopolskii, Yaroslavtsev.     

Synthesis and electrical properties of Gd<Subscript>2</Subscript>MO<Subscript>5</Subscript> (M = Zr,Hf)

Polycrystalline Gd₂ZrO and Gd₂HfO₅ have been prepared by heat-treating coprecipitated oxide mixtures, and their order-disorder phase transitions have been studied in the range 20–1600°C. The materials have been shown to consist of nanostructured grains with a nanodomain size of ∼40 nm. Their electrical conductivity has been determined by impedance spectroscopy in air between 300 and 1000°C. The 1000°C conductivities of Gd₂ZrO₅ and Gd₂HfO₅ are 3.7 × 10⁻³ and 1.8 × 10⁻³ S/cm, and the respective effective activation energies are 1.37 and 1.56 eV.     

A novel method for producing open-cell Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-ZrO<Subscript>2</Subscript> ceramic foams with controlled cell structure

A novel method was introduced to prepare open-cell Al₂O₃–ZrO₂ ceramic foams with controlled cell structure. This method used epispastic polystyrene (EPS) spheres to array ordered templates and centrifugal slip casting in the interstitial spaces of the EPS template to obtain cell struts with high packing density. Aqueous Al₂O₃–ZrO₂ slurries with up to 50 vol.% solid contents were prepared and centrifuged at acceleration of 2,860g. The effect of the solid contents of slurries on segregation phenomena of different particles and green compact uniformity were investigated. In multiphase system, the settling velocities of Al₂O₃ and ZrO₂ particles were calculated. Theory analysis and calculated results both indicated segregation phenomenon was hindered for slurries with 50 vol.% solid content. The cell struts of sintered products had high green density (61.5%TD), sintered density (99.1%TD) and homogeneous microstructures after sintered at 1,550 °C for 2 h. The cell size and porosity of Al₂O₃–ZrO₂ ceramic foams can be adjusted by changing the size of EPS spheres and the load applied on them during packing, respectively. When the porosity increased from 75.3% to 83.1%, the compressive strength decreases from 3.82 to 2.07 MPa.     

Study of structure and properties of ZnO–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Glasses of the ternary system ZnO–Bi₂O₃–P₂O₅ were prepared and studied in two compositional series 50ZnO–xBi₂O₃–(50 − x)P₂O₅ and (50 − y)ZnO–yBi₂O₃–50P₂O₅. Two distinct glass-forming regions were found in the 50ZnO–xBi₂O₃–(50 − x)P₂O₅ glass series with x = 0–10 and 20–35 mol.% Bi₂O₃. All prepared Bi₂O₃-containing glasses reveal a high chemical durability. Small additions of Bi₂O₃ (∼5 mol.%) improve thermal stability of glasses. All glasses crystallize on heating within the temperature range of 505–583 °C. Structural studies by Raman and ³¹P MAS NMR spectroscopies showed the rapid depolymerisation of phosphate chains within the first region with x = 0–15 and the presence of isolated Q⁰ phosphate units within the second region with x = 20–35. Raman studies showed that bismuth is incorporated in the glass structure in BiO₆ units and their vibrational bands were observed within the spectral region of 350–700 cm⁻¹. The evolution of properties and the spectroscopic data are both in accordance with a network former effect of Bi₂O₃.     

Ce and Eu activated Na<Subscript>2</Subscript>Zn<Subscript>5</Subscript>(PO<Subscript>4</Subscript>)<Subscript>4</Subscript>, a new promising novel phosphor

A new efficient phosphor, Eu²⁺/Eu³⁺ and Ce³⁺ activated Na₂Zn₅(PO₄)₄ has been synthesized by solid-state reaction technique at high temperature. X-ray powder diffraction analysis confirmed the formation of Na₂Zn₅(PO₄)₄ host lattice. Scanning electron microscopy indicated that the microstructure of the phosphor consisted of irregular fine grains with a size of about 0·5–2 μm. Photoluminescence excitation spectrum measurements of Ce³⁺ activated Na₂Zn₅(PO₄)₄ show that the phosphor can be efficiently excited by UV-Vis light from 280 to 310 nm to realize emission in the visible (blue) range due to the 5d-4f transition of Ce³⁺ ions which is applicable for scintillation purpose, whereas Eu²⁺/Eu³⁺ activated Na₂Zn₅(PO₄)₄ phosphor emits blue, green and red emission spectrum shows at 487 nm, 546 nm with a dominant peak at 611 nm respectively, due to Eu²⁺/Eu³⁺ ions which is promising candidate for solid state lighting. Therefore, newly synthesised, by low cost and easy technique prepared, novel phosphors may be useful as RGB phosphor for solid state lighting application.     

Structural model for thermal expansion in MZr2P3O12 (M=Li,Na, K,Rb, Cs)

A structural model is proposed to describe the highly anisotropic thermal expansion in the sodium zirconium phosphate NaZr₂P₃O₁₂ structure as a result of the thermal motion of the polyhedra in the structure. In the proposed model the rotations of the phosphate tetrahedra are coupled to the rotation of the zirconium octahedra. Of the two versions considered, the first one allows angular distortions to occur only in the ZrO₆ octahedra; the second one permits all polyhedra to be distorted.     

Low-firing Li<Subscript>2</Subscript>ZnTi<Subscript>3</Subscript>O<Subscript>8</Subscript> microwave dielectric ceramics with BaCu(B<Subscript>2</Subscript>O<Subscript>5</Subscript>) additive

Phase purity, microstructure, sinterability and microwave dielectric properties of BaCu(B₂O₅)-added Li₂ZnTi₃O₈ ceramics and their cofireability with Ag electrode were investigated. A small amount of BaCu (B₂O₅) can effectively reduce the sintering temperature from 1075°C to 925°C, and it does not induce much degradation of the microwave dielectric properties. Microwave dielectric properties of ε _r = 23·1, Q × f = 22,732 GHz and τ _f = − 17·6 ppm/°C were obtained for Li₂ZnTi₃O₈ ceramic with 1·5 wt% BaCu(B₂O₅) sintered at 925°C for 4 h. The Li₂ZnTi₃O₈ +BCB ceramics can be compatible with Ag electrode, which makes it a promising microwave dielectric material for low-temperature co-fired ceramic technology application.     

Formation and properties of SnO–MgO–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

A new glass system SnO–MgO–P₂O₅ with low viscosity has been developed by a melt-quenching method. Formation, thermal properties, and chemical durability of these glasses have been investigated. For a constant P₂O₅ concentration, the glass formation ability is enhanced with the increasing Sn/(Sn + Mg) ratio. The glasses exhibit low glass transition temperature (T _g = 270–400 °C), low dilatometric softening temperature (T _DS = 290–420 °C), and high thermal expansion coefficient (CTE = 110–160 × 10⁻⁷ K⁻¹). With the increasing Sn/(Sn + Mg) ratio, T _g and T _DS decrease, and CTE increases. When Sn/(Sn + Mg) ratio is varied, the relationship between chemical durability and thermal properties of the present glasses is not consistent with what expected in general cases. It is noted that the glasses with 32–32.5 mol% P₂O₅ exhibit excellent chemical durability and tunable T _g, T _DS, and CTE (by varying Sn/(Sn + Mg) ratio).     

Crack propagation in layered Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/ZrO<Subscript>2</Subscript> composites prepared by electrophoretic deposition

Crack propagation through layered Al₂O₃/ZrO₂ composites was studied. The specimens were prepared via electrophoretic deposition of alumina and zirconia powders from suspensions with monochloroacetic acid and isopropanol. The kinetics of electrophoretic deposition could be described fully if the electrophoretic mobility and conductivity of suspensions were known. The conductivity of suspensions increased in the course of deposition. Adjusting to properly controlled kinetics of deposition and sintering, deposits were prepared with strongly bonded layers of different pre-defined thicknesses and, consequently, with different magnitudes of residual stress. Cracks, produced by an indentation technique, propagated askew towards layer interfaces deflected towards the interface in the Al₂O₃ layers and away from the interface in the ZrO₂ layers. Changes in the direction of crack propagation were described for the whole range of angles of incidence (0°–90°). The biggest change in the crack propagation was observed for the angle of incidence 45° and was ca. 15°, irrespective of the magnitude of residual stress in the layers.