Characterization of SiO2–Na2O–Fe2O 3–CaO–P2O 5–B 2O 3 glass ceramics

Bioactivity and magnetic properties were investigated in glass and glass ceramics based on the SiO₂–Na₂O–Fe₂O₃–CaO–P₂O₅–B₂O₃ system to find their suitability as thermoseed for hyperthermia treatment of cancer. The effect of change in compositions on bioactivity was examined in simulated body fluids. The glass ceramic samples exhibit Na₃CaSi₃O₈ and Na_3-XFe_XPO₄ phases. After dipping the glass ceramic samples in simulated body fluids silica hydrogel first forms, followed by an amorphous calcium phosphate layer. Magnetic and microwave resonance experiments further demonstrate the potential of these glass ceramics for possible use in hyperthermia.     

Synthesis of ZnFe2O4–Zn2ZrO4Solid Solutions

Low-temperature plasma synthesis was used to prepare solid solutions ( and ) in the ZnFe₂O₄–Zn₂ZrO₄pseudobinary system. The Zn_{2 – x} Zr_{1 – x} Fe_2x O₄solid solutions were found to have a tetragonal spinel structure (a= 8.607–8.740 Å, c= 8.798–9.120 Å) in the composition range x= 0–0.55 and a cubic spinel structure (a= 8.447–8.539 Å) at x= 0.75–1.0. The tetragonal lattice distortion is attributed to a pseudo-Jahn–Teller effect. The electrical conductivity of the solid solutions shows semiconducting behavior and rises by a few orders of magnitude with increasing Fe³⁺content.     

Li2O–ZnO–Co3O4–TiO2 composite thin-film electrocatalyst for efficient water oxidation catalysis

Thin films of different Li₂O–ZnO–Co₃O₄–TiO₂ (LZCT) compositions were prepared and employed as electrocatalysts (i.e., anodes) to perform water oxidation reaction (WOR). The electrocatalytic activities of these thin films were compared with those exhibited by the sodium salt of cobalt phosphate (Na₂CoP₂O₇) (CP) thin-film electrocatalyst, which is a well-known water oxidation catalyst (WOC). These results suggest that the 10Li₂O–10ZnO–40Co₃O₄–40TiO₂ composition exhibits a better catalytic activity in terms of higher faradaic efficiency (>98%), lower over potentials (<400?mV), higher reaction stability (up to 30 continuous cyclic voltammetry (CV) cycles), and the rate of O₂ and H₂ gas evolution in terms of current density (about 1?mA/cm²) in comparison with those exhibited by CP thin-film electrocatalyst. Furthermore, these LZCT thin films exhibited very high specific surface area values and due to the unique microstructure of ZnCo₂O₄ phase evolved out of these LZCT compositions at a calcination temperature of 550°C for 30?min it has been found to be responsible for the higher specific surface area values measured for these thin-film compositions.     

Phase Relations in the Na2O–Al2O3–Nb2O5and CaO–Al2O3–Nb2O5Systems

Phase relations in the Na₂O–Al₂O₃–Nb₂O₅and CaO–Al₂O₃–Nb₂O₅systems were studied. The Na₂O system was found to contain neither ternary compounds nor niobate–aluminate solid solutions. In the CaO system, a ternary compound of composition 4CaO · Al₂O₃·Nb₂O₅was identified (cubic structure, a= 7.628 Å, Z= 2, _meas= _x= 4.43 g/cm³).     

BaWO4–BaCuO2–Y2Cu2O5–“1010” Section of the Y2O3–BaO–WO3–CuO System

The phase region of cubic perovskite-like solid solutions (a = 8.28–8.40 Å) in the Y₂O₃–BaO–WO₃–CuO system is outlined, and the phase compatibility diagram of the BaWO₄–BaCuO₂–Y₂Cu₂O₅–1010 (1010 = Y₂WO₆ + Y₂W₃O₁₂) is constructed.     

Humidity-sensing properties of ZnCr2O4–ZnO composites

The preparation of ZnCr₂O₄ was carried out by the high-temperature solid-state method with the reaction of Cr₂O₃ and ZnO at 900 °C. Experimental results on the composites made from different mole ratios of ZnCr₂O₄ and ZnO for electrical and humidity-sensing properties are described. The sintered polycrystalline disks of the composites were subjected to DC electrical conductivity measurements over the temperature range 330–500 K from which the activation energies were determined. The composites were identified by powder X-ray diffraction (XRD). The scanning electron microscopy (SEM) studies were carried out to study the surface structure of the sensor materials. The composites were subjected to DC resistance measurements as a function of relative humidity in the range of 5–98% RH, achieved by different water vapor buffers thermostated at room temperature. The sensitivity factor S_f (R_5%/R_98%) measured at 298 K revealed that ZCZO-21 has the highest humidity sensitivity, greater than 6.5×10³; however, ZCZO-11, ZCZO-32, and ZCZO-14 have lower sensitivity but better linear trend. The response and recovery characteristics for ZCZO-21 and ZCZO-11 were assessed.     

Electrical conductivity studies of Bi2O3–Li2O–ZnO–B2O3 glasses

Ac conductivity measurements and its analysis has been performed on xBi₂O₃–(65?x)Li₂O–20ZnO–15B₂O₃ (0 ≤ x ≤ 20) glasses in the temperature range 30–300 °C and a frequency range of 100 Hz to 1 MHz. The dc conductivity increased and the activation energy decreased with lithium content. The frequency dependent conductivity has been analyzed employing conductivity and modulus formalisms. The onset of conductivity relaxation shifts towards higher frequencies with temperature. The Almond–West conductivity formalism is used to explain the scaling behavior, and the relaxation mechanism is independent of temperature.     

Characterisation of Ga2O3–Na2O–CaO–ZnO–SiO2 bioactive glasses

The structural role of Gallium (Ga) is investigated when substituted for Zinc (Zn) in a 0.42SiO₂–0.40–xZnO–0.10Na₂O–0.08CaO glass series, (where x = 0.08). Each starting material was amorphous, and the network connectivity (NC) was calculated assuming Ga acts as both a network modifier (1.23), and also as a network former. Assuming a network forming role for Ga the NC increased with increasing Ga concentration throughout the glass series (Control 1.23, TGa-1 2.32 and TGa-2 3.00). X-ray photoelectron spectroscopy confirmed both composition and correlated NC predictions. Raman spectroscopy was employed to investigate Q-structure and found that a shift in wavenumbers occurred as the Ga concentration increased through the glass series, from 933, 951 to 960 cm^?1. Magic angle spinning nuclear magnetic resonance determined a chemical shift from ?73, ?75 to ?77 ppm as the Ga concentration increased, supporting Raman data. These results suggest that Ga acts predominantly as a network former in this particular Zn-silicate system.     

Microwave dielectric properties of 3Li2O–Nb2O5–3TiO2 ceramics with Li2O–V2O5 additions

A new Li₂O–Nb₂O₅–TiO₂ (LNT) ceramic with the Li₂O:Nb₂O₅:TiO₂ mole ratio of 3:1:3 has been investigated. The compound is composed of two phases, the Li₂TiO₃ and “M-phase” solid solution phase. The microwave dielectric ceramic has low sintering temperature (∼1100 °C) and good microwave dielectric properties of a relatively high permittivity (∼51), high Q × f value up to 8700, and small temperature coefficient (∼37 ppm/°C). The low-amount doping of 0.83Li₂O–0.17V₂O₅ (LV) can effectively lower the sintering temperature from 1100 to 900 °C and induce no obvious degradation of the microwave dielectric properties. Typically, the 1 wt.% LV-doped ceramic sintered at 900 °C has better microwave dielectric properties of ε_r = 51.3, Q × f = 7235 GHz, τ _f  = 22 ppm/°C, which suggests that the ceramics can be applied in microwave LTCC devices.     

EPR study of V2O5–P2O5–Li2O glass system

glass system, with 0 < x 50 mol%, was prepared and investigated by EPR method. For low content of V₂O₅ all the spectra present a hyperfine structure typical for isolated V⁴⁺ ions. With the increasing of V₂O₅ content, the EPR absorption signal showing hyperfine structure is superposed by a broad line without hyperfine structure characteristic for clustered ions. At high V₂O₅ content, the vanadium hyperfine structure disappears and only the broad line can be observed in the spectra. Spin Hamiltonian parameters g , g , A , A , dipolar hyperfine coupling parameters, P, and Fermi contact interaction parameters, K, have been calculated.The composition dependence of line widths of the first two absorptions from the parallel band and of the broad line characteristic to the cluster formations was also discussed.     

Low temperature cofirable Li2Zn3Ti4O12 microwave dielectric ceramic with Li2O–ZnO–B2O3 glass additive

The effects of Li₂O–ZnO–B₂O₃ (LZB) glass additive on the sintering behavior, phase composition, microstructure and microwave dielectric properties of Li₂Zn₃Ti₄O₁₂ ceramics were investigated. The addition of a small amount of LZB glass can reduce the sintering temperature of Li₂Zn₃Ti₄O₁₂ ceramics from 1,075 to 900 °C without much degradation of the microwave dielectric properties. Only a single-phase Li₂Zn₃Ti₄O₁₂ is formed in Li₂Zn₃Ti₄O₁₂ ceramic with LZB addition. Typically, the 1.5 wt% LZB glass-added Li₂Zn₃Ti₄O₁₂ ceramic sintered at 900 °C for 2 h can reach a high relative density of 97.5 % and exhibits good microwave dielectric properties, i.e., relative dielectric constant (ε _r ) = 19.1, quality factor (Q) = 7083.5 at 9 GHz, and temperature coefficient of resonant frequency (τ _f ) = ? 48.9 ppm/°C. In addition, the ceramic could be co-fired well with an Ag electrode, which is made it as a promising dielectric ceramic for low temperature co-fired ceramics technology application.     

Microwave dielectric properties of CaO–La2O3–Nb2O5–TiO2 ceramics

A series of ceramics with a general formula Ca_1+xLa_4?xNb_xTi_5?xO₁₇ (0 ≤ x ≤ 4) were fabricated using the solid-state ceramic route. The phase, microstructure, and microwave dielectric properties varied distinctly with composition or the value of x. X-ray diffraction results showed that the two end member phases, CaLa₄Ti₅O₁₇ and Ca₅Nb₄TiO₁₇, crystallized into single phases with orthorhombic and monoclinic crystal structure, respectively. For intermediate compounds with x = 1, 2, and 3, mixture phases CaLa₄Ti₅O₁₇ and Ca₅Nb₄TiO₁₇ coexisted and a trace amount of second phase was detected. The ceramics showed high ε _r in the range of 45–52, relatively high quality factors with Q × f in the range of 9,870–15,680 GHz and τ _f value in the range between ?38 and ?126.4 ppm/°C. τ _f of CaLa₄Ti₅O₁₇ can be tuned to a near-zero value by addition of suitable amount of TiO₂.     

Improved microwave dielectric properties of Mg4Nb2O9 ceramics with CaO–B2O3–SiO2 glass additions

The effects of CaO–B₂O₃–SiO₂ (CBS) glass addition on the sintering temperature and dielectric properties of Mg₄Nb₂O₉ ceramics have been investigated using X-ray diffraction, Scanning electron microscopy and Differential thermal analysis. The CBS glass can change to liquid phase at about 750 °C and a small amount of CBS glass addition to Mg₄Nb₂O₉ ceramics can greatly decrease the sintering temperature to about 1,125 °C. It is revealed that the reduced sintering temperature is attributed to the formation of liquid phase. The major phases of the sample are Mg₄Nb₂O₉ and MgNb₂O₆. The relationship between τ _f values and the content of glass additions have the reverse change trends. The Mg₄Nb₂O₉ ceramics with 2wt% glass addition sintered 1,125 °C exhibit good microwave dielectric properties: dielectric constant (ε _r ) of 13 and Q·f value of 69,000 GHz.     

PbGe4O9–MGe4O9 (M = Ba, Sr) and BaGe4O9–SrGe4O9 Solid Solutions

PbGe₄O₉–MGe₄O₉ (M = Ba, Sr) and BaGe₄O₉–SrGe₄O₉ samples prepared via melt solidification and by solid-state reactions were characterized by x-ray diffraction and x-ray microanalysis, and their dielectric, piezoelectric, and pyroelectric properties were studied. The results demonstrate that the presence of BaO or SrO in (1 – x)PbO · xMO · 4GeO₂ starting mixtures stabilizes -PbGe₄O₉. In -PbGe₄O₉ crystals, only 3% of the Pb atoms can be substituted with Ba or Sr. In BaGe₄O₉ and SrGe₄O₉ crystals, the fraction of Ba or Sr atoms substituted with Pb attains 40%. BaGe₄O₉ and SrGe₄O₉ form a continuous series of solid solutions. The ferroelectric phase transition near 140 K and the pyroelectric effect in the samples are due to the presence of -PbGe₄O₉. M_{1 – y} Pb _y Ge₄O₉ and Ba_{1 – x} Sr _x Ge₄O₉ solid solutions, isostructural with -PbGe₄O₉, possess neither ferroelectric nor pyroelectric properties.     

Effect of Bi4B2O9 addition on the sintering temperature and microwave dielectric properties of BaO–Nd2O3–4TiO2 ceramics

The effects of Bi₄B₂O₉ addition on the sintering temperature, phase transition and microwave dielectric properties of BaO–Nd₂O₃–4TiO₂ (BNT) ceramics have been investigated. With 10 wt% Bi₄B₂O₉ addition, the sintering temperature of the BNT ceramics can be lowered down to about 1,150 °C. The secondary phase was observed at the level of 15 wt% Bi₄B₂O₉ addition. The Bi₄B₂O₉ addition can significantly affects the microwave dielectric properties. The Q × f ₀ value is a function of the sintering temperature and the Bi₄B₂O₉ content. For the samples sintered at 1,150 °C, Q × f ₀ value varies from 6,300 to 3,300 GHz as the Bi₄B₂O₉ addition increases from 5 to 20 wt%. The addition of Bi₄B₂O₉ does not induce much degradation in ε_r but modified the τ_f value to near zero. Typically, When 10 wt% Bi₄B₂O₉ is added, the τ_f of the ceramics could be tuned to a near-zero value (~1.2 ppm/°C), a substantial ε_r (~86) and Q × f ₀ (~4,670 GHz) could also be achieved simultaneously. The Bi₄B₂O₉ is an efficient sintering additive to decrease the sintering temperature and tune the τ_f value of the microwave dielectric materials for the practical microwave applications.     

Phase Relations in the Systems Al2TiO5–Fe2O3 , Al2O3–TiO2–Fe2O3 , and Al2TiO5–Cr2O3

Phase relations in the systems Al₂TiO₅–Fe₂O₃, Al₂TiO₅–Cr₂O₃, and Al₂O₃–TiO₂–Fe₂O₃ are investigated, and the composition ranges of pseudobrookite Al_{2 – 2x} M_2x TiO₅ (M = Fe, Cr) solid solutions are determined.     

Study of coercive force for yZnFe2O4–(1 − y)CoFe2O4 magnetic nanoparticles system

The coercive forces are taken out from the loops of magnetisation cycle for yZnFe₂O₄–(1 ? y)CoFe₂O₄ mixed magnetic nanoparticles system (y is the volume fraction of ZnFe₂O₄ particles in yZnFe₂O₄–(1 ? y)CoFe₂O₄ magnetic nanoparticles mixed system). The results show that the coercive force of the system is increasing with the y decreasing and is interpreted by using particles chain model. The number of chains of particles under magnetic field is obtained by comparing the coercive force of the experiment and the theory of chain model. In yZnFe₂O₄–(1 ? y)CoFe₂O₄ magnetic nanoparticles mixed system, the coercive force comes from ferrimagnetic CoFe₂O₄ nanoparticles, and paramagnetic ZnFe₂O₄ nanoparticles make the chain length of the mixed magnetic system shorter than single CoFe₂O₄ nanoparticles system.     

On the development of two characteristically different crystal morphology in SiO2–MgO–Al2O3–K2O–B2O3–F glass-ceramic system

The present work demonstrates how crystals with two different characteristic morphologies can be formed in SiO₂–MgO–Al₂O₃–K₂O–B₂O₃–F glass-ceramic system by adopting two sets of heat treatment experiments. In our study, single stage heat treatment experiments were performed at 1,000°C for varying holding time of 8–24 h with 4 h time interval and as a function of temperature in the range of 1,000–1,120°C with 40°C temperature interval. The constant heating rate of 10°C/min was employed for both sets of experiments. The microstructural changes were investigated using Fourier transformed infrared spectroscopy (FT-IR), SEM-EDS and XRD. For temperature variation batches, the microstructure is characterized by interlocked, randomly oriented mica plates (‘house-of-cards’ morphology). An important and new observation of complex crystal morphology is made in the samples heat treated at 1,000°C for varying holding times. Such morphology appears to be the results of composite spherulitic-dendritic like growth of mica rods radiating from a central nucleus. The possible mechanism for such characteristic crystal growth morphology is discussed with reference to a nucleation-growth kinetics based model. The activation energy for crystal nucleation and Avrami index are computed to be 388 kJ/mol and 1.3 respectively, assuming Johnson–Mehl–Avrami model of crystallization. Another important result is that a maximum of around 70% of spherulitic-dendritic like crystal morphology can be obtained after heat treatment at 1,000°C for 24 h, while a lower amount (~58%) of interlocked plate like mica crystals is formed after heat treatment at 1,040°C for 4 h.     

Wurtzite-derived ternary I–III–O2 semiconductors

Ternary zincblende-derived I–III–VI₂ chalcogenide and II–IV–V₂ pnictide semiconductors have been widely studied and some have been put to practical use. In contrast to the extensive research on these semiconductors, previous studies into ternary I–III–O₂ oxide semiconductors with a wurtzite-derived β-NaFeO₂ structure are limited. Wurtzite-derived β-LiGaO₂ and β-AgGaO₂ form alloys with ZnO and the band gap of ZnO can be controlled to include the visible and ultraviolet regions. β-CuGaO₂, which has a direct band gap of 1.47 eV, has been proposed for use as a light absorber in thin film solar cells. These ternary oxides may thus allow new applications for oxide semiconductors. However, information about wurtzite-derived ternary I–III–O₂ semiconductors is still limited. In this paper we review previous studies on β-LiGaO₂, β-AgGaO₂ and β-CuGaO₂ to determine guiding principles for the development of wurtzite-derived I–III–O₂ semiconductors.     

Brazing continuous carbon fiber reinforced Li2O–Al2O3–SiO2 ceramic matrix composites to Ti–6Al–4V alloy using Ag–Cu–Ti active filler metal

C_f/LAS composites and TC4 alloy were brazed successfully by vacuum brazing using Ag–Cu–Ti active filler metal. The interfacial microstructure was characterized by a scanning electron microscope, energy dispersive spectrometer and X-ray diffraction. The effects of brazing temperature on the interfacial microstructure and joint properties were investigated in details. Various phases including TiC, TiSi₂, Ti₃Cu₄, Cu (s,s), Ag (s,s), TiCu and Ti₂Cu were formed in the brazed joints. Interfacial microstructure varies greatly with the increase of brazing temperature, while the amount of Ti₂Cu reduced, but no new phase is generated. The optimal shear strength of the joint is 26.4 MPa when brazed at 890 °C for 10 min. Shear test indicated that the fracture of the brazed joints went through the TiSi₂ + TiC layer close to the C_f/LAS composites interface.