Giant electrical conductivity enhancement in BaO–V2O5–Bi2O3 glass by nanocrystallization

The effects of the annealing of 20BaO–30V₂O₅–50Bi₂O₃ glass on the structural and electrical properties were studied by scanning electron micrographs (SEM), X-ray diffraction (XRD), differential scanning calorimeter (DSC) density (d) and dc conductivity (σ). The XRD and SEM observations have shown that the sample under study undergoes structural changes: from amorphous at the beginning, to partly crystalline after nanocrystallization at crystallization temperature (T_c) for 1 h and to colossal crystallization after the annealing at the same temperature for 24 h. The average size of these grains after nanocrystallization at T_c for 1 h was estimated to be about 25–35 nm. However, the glass heat treated at T_c = 580 °C for 24 h the microstructure changes considerably. The nanomaterials obtained by nanocrystallization at T_c for 1 h exhibit giant improvement of electrical conductivity up to four order of magnitude and better thermal stability than the as-received glass. The major role in the conductivity enhancement of this nanomaterial is played by the developed interfacial regions “conduction tissue” between crystalline and amorphous phases, in which the concentration of V⁴⁺–V⁵⁺ pairs responsible for electron hopping is higher than inside the glassy matrix. The annealing at T_c for 24 h leads to decrease of the electronic conductivity. This phenomena lead to disappearance of the abovementioned “conduction tissue” for electrons and substantial reduction of electronic conductivity. The high temperature (above θ/2) dependence of conductivity could be qualitatively explained by the small polaron hopping (SPH) model. The physical parameters obtained from the best fits of this model are found reasonable and consistent with the glass compositions.     

Relaxation process in PbI2–Ag2O–V2O5–B2O3 system: Dielectric,AC conductivity and modulus studies

Silver ion conducting super-ionic glass system xPbI₂–(100 − x) [Ag₂O–2(V₂O₅–B₂O₃)], where, 5 ≤ x ≤ 25, were prepared via melt quenching route and -characterized by XRD and DSC. Their electrical properties were measured by impedance spectroscopy in the frequency range of 2 MHz to 20 Hz from 30 to 120 °C. The electrical relaxation mechanism has been studied using AC conductivity, dielectric modulus function and frequency dependent dielectric permittivity over a wide range of frequency and temperature. Two different scaling approaches for AC conductivity as well as dielectric permittivity spectra were used to understand the nature of relaxation processes.     

Thermal properties and crystallization of PbO–MoO3–P2O5 glasses

Thermal properties and crystallization of glasses from PbO–MoO₃–P₂O₅ ternary system were studied in three compositional series (100 − x)[0.5PbO–0.5P₂O₅]–xMoO₃ (A), 50PbO–yMoO₃–(50 − y)P₂O₅ (B), and (50 − z)PbO–zMoO₃–50P₂O₅ (C). Glass transition temperature, crystallization temperature, coefficient of thermal expansion, and dilatation softening temperature of the studied glasses were determined by differential thermal analysis and dilatometry. Crystallization products of annealed glass samples were investigated by X-ray diffraction and Raman spectroscopy. X-ray diffraction analysis of crystallized glasses revealed the formation of PbP₂O₆, Pb₃P₄O₁₃, and PbMoO₄ in the samples of the B series. In the series A and C in the samples with a high MoO₃ content, crystalline compounds of Pb(MoO₂)₂(PO₄)₂ and (MoO₂)(PO₃)₂, respectively, were identified. Raman spectra of crystalline samples confirmed the results of X-ray diffraction measurements and provided also information on thermal stability of glasses and formation of glass-crystalline phases in the studied glass series.     

Structural and dielectric properties of Li2O–ZnO–BaO–B2O3–CuO glasses

Glass samples of the system (15Li₂O–30ZnO–10BaO–(45 − x)B₂O₃–xCuO where x = 0, 5, 10 and 15 mol%) were prepared by using the melt quenching technique. A number of studies, viz. density, differential thermal analysis, FT-IR spectra, a.c. conductivity and dielectric properties (constant εφ, loss tan δ, a.c. conductivity, σ_ac, over a wide range of frequency and temperature) of these glasses were carried out as a function of copper ion concentration. The analysis of the results indicate that the density increases while molar volume decreases with increasing of copper content indicates structural changes of the glass matrix. The glass transition temperature, T _g, and crystallization temperature, T _c, increase with the variation of concentration of CuO referred to the growth in the network connectivity in this concentration range, while glass-forming ability parameter (T _c − T _g) decreases with increasing CuO content, indicates an increasing concentration of copper ions that take part in the network-modifying positions. The FT-IR spectra evidenced that the main structural units are BO₃, BO₄, and ZnO₄. The structural changes observed by varying the CuO content in these glasses and evidenced by FTIR investigation suggest that the CuO plays a network modifier role in these glasses while ZnO plays the role of network formers. The dielectric constant decreased with increase in temperature and CuO content. The variation of a.c. conductivity with the concentration of CuO passes through a maximum at 5 mol%. In the high temperature region, the a.c. conduction seems to be connected with the mixed conduction viz., electronic conduction and ionic conduction.     

Densification and dielectric properties of SrO–Al2O3–B2O3 ceramic bodies

The influence of SrO (0·0–5·0 wt%) on partial substitution of alpha alumina (corundum) in ceramic composition (95 Al₂O₃–5B₂O₃) have been studied by co-precipitated process and their phase composition, microstructure, microchemistry and microwave dielectric properties were studied. Phase composition was revealed by XRD, while microstructure and microchemistry were investigated by electron-probe microanalysis (EPMA). The dielectric properties by means of dielectric constant (ε _r ), quality factor (Q × f) and temperature coefficient of resonant frequency (τ _f ) were measured in the microwave frequency region using a network analyser by the resonance method. The addition of B₂O₃ and SrO significantly reduced the sintering temperature of alumina ceramic bodies to 1600 °C with optimum density (∼ 4g/cm³) as compared with pure alumina powders recycled from Al dross (3·55g/cm³ sintered at 1700 °C).     

Synthesis and properties of glasses in the K2O–SiO2–Bi2O3–TiO2 system and bismuth titanate (Bi4Ti3O12) nano glass–ceramics thereof

Glasses were prepared by the melt-quench technique in the K₂O–SiO₂–Bi₂O₃–TiO₂ (KSBT) system and crystallized bismuth titanate, BiT (Bi₄Ti₃O₁₂) phase in it by controlled heat-treatment at various temperature and duration. Different physical, thermal, optical, and third-order susceptibility (χ³) of the glasses were evaluated and correlated with their composition. Systematic increase in refractive index (n) and χ³ with increase in BiT content is attributed to the combined effects of high polarization and ionic refraction of bismuth and titanium ions. Microstructural evaluation by FESEM shows the formation of polycrystalline spherical particles of 70–90 nm along with nano-rods of average diameter of 85–90 nm after prolonged heat treatment. A minor increase in dielectric constants (ε_r) has been observed with increase in polarizable components of BiT in the glasses, whereas a sharp increase in ε_r in glass–ceramics is found to be caused by the formation of non-centrosymmetric and ferroelectric BiT nanocrystals in the glass matrix.     

Optical properties and structure of R2O–Ga2O3–SiO2 and RO–Ga2O3–SiO2 glasses

Refractive index and molar refraction of Li₂O–, Na₂O–, CaO–, and BaO–Ga₂O₃–SiO₂ glasses have been used to test the validity of a structural model of silicate glasses containing Ga₂O₃ glasses. Ga₂O₃ enters these types of glass in a similar manner as Al₂O₃. It is assumed that, for (SiO₂/Ga₂O₃) >1 and (Ga₂O₃/R₂O) ≤1, Ga₂O₃ associates primarily with modifier oxides to form GaO₄ units. The rest of modifier oxide forms silicate units with non-bridging oxygen ions. Silicate structural units have the same factors as found for binary alkali- and alkaline earth silicate glasses. Differences between experimental and model values suggest another structure for (Ga₂O₃/SiO₂) ≥1.     

Glass formation and third-order optical nonlinear characteristics of bismuthate glasses within Bi2O3–GeO2–TiO2 pseudo-ternary system

Glass-forming region of Bi₂O₃–GeO₂–TiO₂ (BGT) pseudo-ternary system was determined by using melt-quench method. A series of high transparent glass samples were selected and their structural characteristics were investigated by FT-IR and Raman spectra. By employing Z-scan and optical Kerr shutter techniques with femtosecond laser pulses as excitation source, third-order optical nonlinearities (TON) of the BGT glasses as well as the TON response time were investigated at wavelength of 800 nm. The ultrafast nonlinear response and high figure of merit suggest great potentials of BGT glasses in applications of all-optical switching or related optical devices.     

Structure and electrical properties of Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–BiCoO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x − y)Bi_0.5Na_0.5TiO₃–xBi_0.5K_0.5TiO₃–yBiCoO₃ (x = 0.12–0.24, y = 0–0.04) have been fabricated by a conventional solid-state reaction method, and their structure and electrical properties have been investigated. The XRD analysis shows that samples with y ≤ 0.03 exhibit a pure perovskite phase and very weak impurity reflections can be detected in the sample with y = 0.04. With x increasing from 0.12 to 0.24 and y increasing from 0 to 0.04, the ceramics transform gradually from a rhombohedral phase to a tetragonal phase and rhombohedral–tetragonal phase coexistence to a pseudocubic phase, respectively. The morphotropic phase boundary (MPB) of the system between rhombohedral and tetragonal locates in the range of x = 0.18–0.21, y = 0–0.03. The ceramics near the composition of the MPB have good performances with piezoelectric constant d ₃₃ = 156 pC/N and electromechanical coupling factor k _p = 0.34 at x = 0.21 and y = 0.01, which attains a maximum value in this ternary system. Adding content of BiCoO₃ leads to a disappearance of the response in the curves of dielectric constant-temperature to the ferroelectric–antiferroelectric transition. The temperature dependence of dielectric properties suggests that the ceramics are relaxor ferroelectrics. The results show that (1 − x − y)Bi_0.5Na_0.5TiO₃–xBi_0.5K_0.5TiO₃–yBiCoO₃ ceramics are good candidate for use as lead-free ceramics.     

Sol–gel derived CaO–B2O3–SiO2 glass/CaSiO3 ceramic composites: processing and electrical properties

The CaO–B₂O₃–SiO₂ glass/CaSiO₃ ceramic (CBS/CS) composites were fabricated via sol–gel processing routes. Their densification behavior, structures and dielectric properties were investigated. The precursors of CBS glass and CS ceramic filler were firstly obtained via individual soft chemical route and then mixed together in various proportions. The results indicated that the structures of CBS/CS composites are characteristic of CS and CaB₂O₄ (CB) ceramic phases distributed in the matrix of glass phase at 800–950 °C. The CS ceramic phase not only acts as fillers, but nuclei for the crystallization of CBS glass as well such that the CS content exhibits an effect on the densification and dielectric properties of the composites. The CBS/CS composites with 10% CS sintered at 850 °C own dielectric properties of ε_r < 5 and tanδ = 6.4 × 10⁻⁴ at 1 MHz.     

Highlighting of structural units of B2O3–Li2O–P2O5 system under heat treatment

As technology evolves towards the design of small size – high efficiency devices there is a necessity for the development of solid, stable electrolytes that can be fabricated in various shapes. Accordingly, a glass system of xB₂O₃·0.4Li₂O·(0.6 − x)P₂O₅ with 0 ≤ x ≤ 0.6 mol%, was prepared by melting the raw materials at 1200 °C and rapidly cooling the melts at room temperature. The samples were afterwards heat treated to develop crystalline structures, for better identification of the units that build up the network.     

Microstructures formed during devitrification of Na2O·Al2O3·B2O3·SiO2·Fe2O3 glasses

Soda alumina borosilicate glasses of composition (24-y)Na₂O·yAl₂O₃·14B₂O₃·37SiO₂·25Fe₂O₃, y = 8, 12, 14, 16 mol%, were melted using Fe₂O₃ as raw material. Besides, samples with y = 12 and Fe₂O₃ concentrations of 14.32, 17.8, and 25.0 mol% were prepared from FeC₂O₄·2H₂O as raw material. The X-ray diffraction analyses showed the presence of magnetite for the samples from all the investigated compositions. Transmission electron microscopy (TEM) evidenced that all the samples are phase separated and droplets in the diameter range 100–1000 nm, enriched in iron, are formed. Inside these droplets, numerous small magnetite particles, with size in the 25–40 nm interval, are crystallized.     

Synthesis and properties of magnetic solid superacid: SO4/ZrO2–B2O3–Fe3O4

A magnetic SO₄²⁻/ZrO₂–B₂O₃–Fe₃O₄ solid superacid catalyst is prepared via a simple chemical co-precipitation approach. The obtained materials were characterized in detailed by X-ray powder diffraction, thermogravimetric analysis–different scanning calorimetry, Fourier transform infrared spectroscopy (FTIR), electron microscopy (SEM and TEM), and Mossbauer spectra. Powder X-ray diffraction patterns show that in this composite oxide the transformation temperature of ZrO₂ from tetragonal to monoclinic phase is higher compared to the pristine SO₄²⁻/ZrO₂ material. The introduction of Fe₃O₄ endows the superacid with a super-paramagnetic property while in a ferromagnetic state after calcination. The superacid exhibits high catalytic activity in forming ethyl acetate by esterification.     

Low-temperature sintering and microwave dielectric properties of 5Li2O–0.58Nb2O5–3.23TiO2 ceramics

The effect of B₂O₃ addition on the sintering, microstructure and the microwave dielectric properties of the 5Li₂O–0.58Nb₂O₅–3.23TiO₂ (LNT) ceramics have been investigated. It is found that the LNT ceramics could be sintered well at ∼880 °C with low-level doping of B₂O₃ (≤2 wt.%). Only Li₂TiO₃ solid solution (Li₂TiO₃ss) crystal structure could be detected for all the ceramics with various amounts of B₂O₃ addition from the X-ray diffraction (XRD) results. And interestingly, two phases with different color in SEM images are observed in B₂O₃-doped LNT ceramics. EDS results suggest that the two different phases are two Li₂TiO₃ss phases with different amount of Nb. In addition, there is no much degradation in the microwave dielectric properties with the B₂O₃ adding. In the case of 0.5 wt.% B₂O₃-doped samples sintered at 880 °C, good microwave dielectric properties of ?_r = 22, Q × f = 32,000 GHz, τ_f = 9.5 ppm °C⁻¹ are obtained.     

Structure study of MoO3-ZnO-B2O3 glasses by Raman spectroscopy and formation of α-ZnMoO4 nanocrystals

Molybdenum oxide (MoO₃)-containing glasses of xMoO₃-50ZnO-(50−x)B₂O₃ (x = 10, 20, and 30) are prepared using a conventional melt quenching method, and the glass structure and crystallization behaviour are clarified. It is found that the thermal stability against crystallization of the glasses decreases drastically with increasing MoO₃ content. The main valence of Mo ions in the glasses is found to be Mo⁶⁺ from X-ray photoelectron spectroscopy measurements. The Raman bands observed at ∼860 cm⁻¹ and 950 cm⁻¹ suggest that the coordination state of Mo⁶⁺ ions in the glasses is mainly (MoO₄)²⁻ tetrahedral units. All glasses examined in this study give the formation of α-ZnMoO₄ as the initial crystalline phase. In particular, 30MoO₃-50ZnO-20B₂O₃ glass shows the bulk crystallization of α-ZnMoO₄ nanocrystals with a diameter of ∼5 nm. The crystallized glasses consisting of Eu³⁺-doped ZnMoO₄ crystals are synthesized, and enhanced photoluminescence emissions (i.e., the quantum yield is 9%) due to the 4f transitions ⁵D₀ → ⁷F_J (J = 0-4) of Eu³⁺ ions is observed.     

Investigation on the phase stability,sintering and thermal conductivity of Sc2O3–Y2O3–ZrO2 for thermal barrier coating application

Rare earth oxides co-doped zirconia have been developed for application in thermal barrier coating systems to promote the performance and durability of gas turbines. 8 mol%Sc₂O₃, 0.6 mol%Y₂O₃–stabilized ZrO₂ (ScYSZ) powder was synthesized by chemical co-precipitation method. The phase stability, sintering resistance and thermo-physical properties of ScYSZ and 8 wt%Y₂O₃ stabilized ZrO₂ (8YSZ) were investigated. The results indicated that both ScYSZ and 8YSZ show single tetragonal phase before heat treatment. After heat treating at 1500 °C for 300 h, ScYSZ exhibits excellent phase stability with 100% metastable tetragonal (t′) phase, whereas the content of monoclinic phase in 8YSZ reached 49.4 mol%. ScYSZ also exhibits higher sintering resistance and lower thermal conductivity than 8YSZ. ScYSZ can be considered to be explored as candidate material for TBC application.     

Structure and ac conductivity of sodium–lead–cadmium metaphosphate glasses

Sodium–lead–cadmium phosphate glasses having a mol% composition (40−y)Na₂O–yCdO–10PbO–50P₂O₅ (0≤y≤40) were prepared by using the melt–quench technique. They have been characterised by infrared spectroscopy, Raman spectroscopy and ³¹P magic angle spinning nuclear magnetic resonance (MAS-NMR). Infrared and Raman spectroscopies reveal the formation of P–O–Pb and P–O–Cd bonds, which replace P–O–⁺Na bonds. MAS-NMR spectroscopy shows that no metaphosphate network depolymerisation occurs when y increases. Thus, both PbO and CdO act as the network modifiers. Systematic variations of the glass transition temperature, density, and molar volume observed are in agreement with these results. Ionic conductivity is correlated to the structural model.     

Dielectric properties and microstructure of TiO2 modified (ZnMg)TiO3 microwave ceramics with CaO–B2O3–SiO2

The low-fired (ZnMg)TiO₃–TiO₂ (ZMT–TiO₂) microwave ceramics using low melting point CaO–B₂O₃–SiO₂ as sintering aids have been developed. The influences of Mg substituted fraction on the crystal structure and microwave properties of (Zn_1−x Mg _x )TiO₃ were investigated. The result reveals that the sufficient amount of Mg (x ≥ 0.3) could inhibit the decomposition of ZnTiO₃ effectively, and form the single-phase (ZnMg)TiO₃ at higher sintering temperatures. Due to the compensating effect of rutile TiO₂ (τ_f = 450 ppm/°C), the temperature coefficient of resonant frequency (τ_f) for (Zn_0.65Mg_0.35)TiO₃–0.15TiO₂ with biphasic structure was adjusted to near zero value. Further, CaO–B₂O₃–SiO₂ addition could reduce the sintering temperature from 1150 to 950 °C, and significantly improve the sinterability and microwave properties of ZMT–TiO₂ ceramics, which is attributed to the formation of liquid phases during the sintering process observed by SEM. The (Zn_0.65Mg_0.35)TiO₃–0.15TiO₂ dielectrics with 1 wt% CaO–B₂O₃–SiO₂ sintered at 950 °C exhibited the optimal microwave properties: ε ≈ 25, Q × f ≈ 47,000 GHz, and τ_f ≈ ± 10 ppm/°C.