Experimental Measurements of Thermophysical Properties of \mathrm{Al}_{2}\mathrm{O}_{3}– and \mathrm{TiO}_{2}–Ethylene Glycol Nanofluids

This paper presents measurements of the thermal conductivity and the dynamic viscosity of $\mathrm{Al}_{2}\mathrm{O}_{3}$ Al 2 O 3 –ethylene glycol and $\mathrm{TiO}_{2}$ TiO 2 –ethylene glycol (1 % to 3 % particle volume fraction) nanofluids carried out in the temperature range from $0\,^{\circ }$ 0 ° C to $50\,^{\circ }$ 50 ° C. The thermal-conductivity measurements were performed by using a transient hot-disk TPS 2500S apparatus instrumented with a 7577 probe (2.001 mm in radius) having a maximum uncertainty $(k=2)$ ( k = 2 ) lower than 5.0 % of the reading. The dynamic-viscosity measurements and the rheological analysis were carried out by a rotating disk type rheometer Haake Mars II instrumented with a single-cone probe (60 mm in diameter and $1^{\circ }$ 1 ° ) having a maximum uncertainty $(k=2)$ ( k = 2 ) lower than 5.0 % of the reading. The thermal-conductivity measurements of the tested nanofluids show a great sensitivity to particle volume fraction and a lower sensitivity to temperature: $\mathrm{TiO}_{2}$ TiO 2 –ethylene glycol and $\mathrm{Al}_{2}\mathrm{O}_{3}$ Al 2 O 3 –ethylene glycol nanofluids show a thermal-conductivity enhancement (with respect to pure ethylene glycol) from 1 % to 19.5 % and from 9 % to 29 %, respectively. $\mathrm{TiO}_{2}$ TiO 2 –ethylene glycol and $\mathrm{Al}_{2}\mathrm{O}_{3}$ Al 2 O 3 –ethylene glycol nanofluids exhibit Newtonian behavior in all the investigated temperature and particle volume fraction ranges. The relative viscosity shows a great sensitivity to the particle volume fraction and weak or no sensitivity to temperature: $\mathrm{TiO}_{2}$ TiO 2 –ethylene glycol and $\mathrm{Al}_{2}\mathrm{O}_{3}$ Al 2 O 3 –ethylene glycol nanofluids show a dynamic viscosity increase with respect to ethylene glycol from (4 to 5) % to 30 % and from 14 % to 50 %, respectively. Present experimental measurements were compared both with available measurements carried out by different researchers and computational models for thermophysical properties of nanofluids.     

Fusion Diagrams in the \mathrm{BiBO}_{3}–\mathrm{YbBO}_{3} and \mathrm{Bi}_{4}\mathrm{B}_{2}\mathrm{O}_{9}–\mathrm{YbBO}_{3} Systems

A calculation model of the Gibbs energy of ternary oxide compounds from the binary components was used. Thermodynamic properties of \(\mathrm{Yb}_{2} \mathrm{O}_{3}\) – \(\mathrm{Bi}_{2}\mathrm{O}_{3}\) – \(\mathrm{B}_{2}\mathrm{O}_{3}\) ternary systems in the condensed state were calculated. Thermodynamic data of binary and ternary compounds were used to determine the stable sections. The probability of reactions between the corresponding components in the \(\mathrm{Yb}_{2} \mathrm{O}_{3}\) – \(\mathrm{Bi}_{2} \mathrm{O}_{3}\) – \(\mathrm{B}_{2} \mathrm{O}_{3}\) system was estimated. Fusibility diagrams of systems \(\mathrm{BiBO}_{3}\) – \(\mathrm{YbBO}_{3}\) and \(\mathrm{Bi}_{4} \mathrm{B}_{2} \mathrm{O}_{9}\) – \(\mathrm{YbBO}_{3}\) were studied by physical–chemical analysis. The isothermal section of the phase diagram of \(\mathrm{Yb}_{2} \mathrm{O}_{3}\) – \(\mathrm{Bi}_{2} \mathrm{O}_{3}\) – \(\mathrm{B}_{2} \mathrm{O}_{3}\) at 298 K is built, as well as the projection of the liquid surface of \(\mathrm{BiBO}_{3}\) – \(\mathrm{B}_{2} \mathrm{O}_{3}\) – \(\mathrm{YbBO}_{3}\) .     

Radiative Properties of Ceramic $$\hbox {Al}_{2}\hbox {O}_{3}$$, AlN and $$\hbox {Si}_{3}\hbox {N}_{4}$$Si3N4—II: Modeling

In Part I of this study (Cheng et al. in Int J Thermophys 37: 62, 2016), the reflectance and transmittance of dense ceramic plates were measured at wavelengths from 0.4 \(\upmu \hbox {m}\) to about 20 \(\upmu \hbox {m}\). The samples of \(\hbox {Al}_{2}\hbox {O}_{3}\) and AlN are semitransparent in the wavelength region from 0.4 \(\upmu \hbox {m}\) to about 7 \(\upmu \hbox {m}\), where volume scattering dominates the absorption and scattering behaviors. On the other hand, the \(\hbox {Si}_{3}\hbox {N}_{4}\) plate is opaque in the whole wavelength region. In the mid-infrared region, all samples show phonon vibration bands and surface reflection appears to be strong. The present study focuses on modeling the radiative properties and uses an inverse method to obtain the scattering and absorption coefficients of \(\hbox {Al}_{2}\hbox {O}_{3}\) and AlN in the semitransparent region from the measured directional-hemispherical reflectance and transmittance. The scattering coefficient is also predicted using Mie theory for comparison. The Lorentz oscillator model is applied to fit the reflectance spectra of AlN and \(\hbox {Si}_{3}\hbox {N}_{4}\) from 1.6 \(\upmu \hbox {m}\) to 20 \(\upmu \hbox {m}\) in order to obtain their optical constants. It is found that the phonon modes for \(\hbox {Si}_{3}\hbox {N}_{4}\) are much stronger in the polycrystalline sample studied here than in amorphous films reported previously.     

Synthesis of $$\hbox {Ag}_{2}\hbox {Se}$$–graphene–$$\hbox {TiO}_{2} $$TiO2 nanocomposite and analysis of photocatalytic activity of $$\hbox {CO}_{2}$$CO2 reduction to $$\hbox {CH}_{3}\hbox {OH}$$CH3OH

The present work deals with the development of a new ternary composite, \(\hbox {Ag}_{2}\hbox {Se}\)–\(\hbox {G}\)–\(\hbox {TiO}_{2}\), using ultrasonic techniques as well as X-ray diffraction (XRD), scanning electron microscopy (SEM), high transmission electron microscopy (HTEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and UV–Vis diffuse reflectance spectra (DRS) analyses. The photocatalytic potential of nanocomposites is examined for \(\hbox {CO}_{2}\) reduction to methanol under ultraviolet (UV) and visible light irradiation. \(\hbox {Ag}_{2}\hbox {Se}\)–\(\hbox {TiO}_{2}\) with an optimum loading graphene of 10 wt% exhibited the maximum photoactivity, obtaining a total \(\hbox {CH}_{3}\hbox {OH}\) yield of 3.52 \(\upmu \hbox {mol}\,\hbox {g}^{-1}\,\hbox {h}^{-1}\) after 48 h. This outstanding photoreduction activity is due to the positive synergistic relation between \(\hbox {Ag}_{2}\hbox {Se}\) and graphene components in our heterogeneous system.     

In situ synthesis and properties of self-reinforced $$\hbox {Si}_{3} \hbox {N}_{4}\textendash \hbox {SiO}_{2}\textendash \hbox {Al}_{2} \hbox {O}_{3}\textendash \hbox {Y}_{2}\hbox {O}_{3} \ (\hbox {La}_{2}\hbox {O}_{3}$$) glass–ceramic composites

In-situ-grown \(\upbeta \!\hbox {-Si}_{3}\hbox {N}_{4}\)-reinforced \(\hbox {SiO}_{2}\textendash \hbox {Al}_{2}\hbox {O}_{3}\textendash \hbox {Y}_{2}\hbox {O}_{3}\) \((\hbox {La}_{2}\hbox {O}_{3})\) self-reinforced glass–ceramic composites were obtained without any \(\upbeta \!\hbox {-Si}_{3}\hbox {N}_{4}\) seed crystal. These composites with different compositions were prepared in a nitrogen atmosphere for comparison of phase transformation and mechanical properties. The results showed that \(\hbox {SiO}_{2}\textendash \hbox {Al}_{2}\hbox {O}_{3}\textendash \hbox {Y}_{2}\hbox {O}_{3}\) \((\hbox {La}_{2}\hbox {O}_{3})\) glass can effectively promote \(\upalpha \)- to \(\upbeta \!\hbox {-Si}_{3}\hbox {N}_{4}\) phase transformation. The crystallized \(\hbox {Y}_{2}\hbox {Si}_{2}\hbox {O}_{7}\textendash \hbox {La}_{4.67}\hbox {Si}_{3}\hbox {O}_{13}\) phases with a high melting point significantly benefited the high-temperature mechanical properties of the composites. The \(\hbox {Si}_{3}\hbox {N}_{4}\textendash \hbox {SiO}_{2}\textendash \hbox {Al}_{2} \hbox {O}_{3}\textendash \hbox {Y}_{2}\hbox {O}_{3}\) \((\hbox {La}_{2}\hbox {O}_{3})\) glass–ceramic composites exhibit excellent mechanical properties compared with unreinforced glass–ceramic matrix, which is undoubtedly attributed to the elongated \(\upbeta \!\hbox {-Si}_{3}\hbox {N}_{4}\) grains. These glass–ceramic \(\hbox {Si}_{3}\hbox {N}_{4}\) composites with excellent comprehensive properties might be a promising material for high-temperature applications.     

Lattice Dynamical,Elastic and Thermodynamical Properties of III–V Semiconductor AlSb,GaSb and Their Mixed Semiconductor $$\hbox {Ga}_{\mathrm{1-x}}\hbox {Al}_{\mathrm{x}}\hbox {Sb}$$

A proposed eleven-parameter three-body shell model is used to study the lattice dynamical properties such as phonon dispersion relations along high symmetry directions, phonon density of states, variation of specific heat and Debye characteristic temperature with absolute temperature, elastic constants and related properties for III–V semiconductor AlSb, GaSb and their mixed semiconductor \(\hbox {Ga}_{\mathrm{1-x}}\hbox {Al}_{\mathrm{x}}\hbox {Sb}\) having zinc-blende structure. We found an overall good agreement with the available experimental and theoretical results available in the literature.     

Microwave dielectrics: solid solution,ordering and microwave dielectric properties of $$(1{-}x)\hbox {Ba}(\hbox {Mg}_{1/3}\hbox {Nb}_{2/3})\hbox {O}_{3}{-}x\hbox {Ba(Mg}_{1/8}\hbox {Nb}_{3/4})\hbox {O}_{3}$$ ceramics

The effect of Ba(\(\hbox {Mg}_{1/8}\hbox {Nb}_{3/4})\hbox {O}_{3}\) phase on structure and dielectric properties of \(\hbox {Ba(Mg}_{1/3}\hbox {Nb}_{2/3})\hbox {O}_{3}\) was studied by synthesizing \((1{-}x)\hbox {Ba(Mg}_{1/3}\hbox {Nb}_{2/3})\hbox {O}_{3}{-}x\hbox {Ba}(\hbox {Mg}_{1/8}\hbox {Nb}_{3/4})\hbox {O}_{3}\) (\(x = 0\), 0.005, 0.01 and 0.02) ceramics. Superlattice reflections due to 1:2 ordering appear as low as \(1000^{\circ }\hbox {C}\). \(\hbox {Ba}(\hbox {Mg}_{1/3}\hbox {Nb}_{2/3})\hbox {O}_{3}\) forms solid solution with \(\hbox {Ba}(\hbox {Mg}_{1/8}\hbox {Nb}_{3/4})\hbox {O}_{3}\) for all ‘x’ values studied until \(1350^{\circ }\hbox {C}\). Ordering was confirmed by powder X-ray diffraction pattern, Raman study and HRTEM. Ceramic pucks can be sintered to density \({>}92\%\) of theoretical density. Temperature and frequency-stable dielectric constant and nearly zero dielectric loss (tan \(\delta \)) were observed at low frequencies (20 MHz). The sintered samples exhibit dielectric constant (\(\varepsilon _{\mathrm{r}})\) between 30 and 32, high quality factor between 37000 and 74000 GHz and temperature coefficient of resonant frequency (\(\tau _{\mathrm{f}})\) between 21 and \(24\hbox { ppm }^{\circ }\hbox {C}^{-1}\).     

Thermodynamic Investigation of the Eutectic Mixture of the $$\hbox {LiNO}_{3}$$–$$\hbox {NaNO}_{3}$$NaNO3–$$\hbox {KNO}_{3}$$KNO3–$$\hbox {Ca}(\hbox {NO}_{3})_{2}$$Ca(NO3)2 System

Molten nitrate salt is usually employed as heat transfer or energy storage medium in concentrating solar power systems to improve the overall efficiency of thermoelectric conversion. In the present work, the liquidus curves of the \(\hbox {LiNO}_{3}\)–\(\hbox {NaNO}_{3}\)–\(\hbox {KNO}_{3}\)–\(\hbox {Ca}(\hbox {NO}_{3})_{2}\) system is determined by conformal ionic solution theory according to the solid–liquid equilibrium state of the binary mixture. The calculated eutectic temperature of the mixture is \(93.17\,{^{\circ }}\hbox {C}\), which is close to the experimental value of \(93.22\,{^{\circ }}\hbox {C}\) obtained from differential scanning calorimetry (DSC). Visualization observation experiments reveal that the quaternary eutectic mixture begins to partially melt when the temperature reaches \(50\,{^{\circ }}\hbox {C}\), and the degree of melting increases with temperature. The mixture is completely melted at \(\hbox {130}\,{^{\circ }}\hbox {C}\). The observed changes in the dissolved state at different temperatures correlate well with the DSC heat flow curve fluctuations.     

Magnetic measurements,Raman and infrared spectra of metal–ligand complex derived from $$\hbox {CoCl}_{2}\cdot \hbox {6H}_{2}\hbox {O}$$ and 2-benzoyl pyridine

Nanocrystalline complex of \(\hbox {CoCl}_{2}\cdot 6\hbox {H}_{2}\hbox {O}{-}2\)-benzoyl pyridine is prepared by chemical route. Each component of the desired complex is identified by analysing the X-ray diffractograms. Energy-dispersive X-ray analysis (EDX) data confirmed the presence of the desired elements of the sample. Theoretical optimized structure of the complex was derived using ab initio density functional level of theory (DFT) method of calculation. The average nanocrystallite size estimated from the XRD data is \(\sim \)43 nm. Static magnetic property of the complex is studied in the temperature range from 300 K down to 14 K. The estimated magnetic moment of the complex is high when compared to that of the free ion magnetic moment of \(\hbox {Co}^{2+}\) and this is attributed to the less effect of the crystal field acting on the ion in the organic complex due to which orbital moments are not fully quenched. The magnetic property of the complex is also remarkably enhanced compared to that of the diamagnetic 2-benzoyl pyridine which may be suitable for applications in devices. FTIR and Raman spectra of the ligand, 2-benzoyl pyridine and the synthesized complex are recorded at room temperature, which not only confirm the presence of each phase in the complex, but some interesting results are also extracted from the analyses of different Raman active modes of the complex.     

Electrical and Thermal Characteristics of the Insulator–Metal Transition in Crystalline $$\hbox {V}_{2}\hbox {O}_{5}$$ Films

The electrical and thermal properties with respect to the crystallization in \(\hbox {V}_{2}\hbox {O}_{5}\) thin films were investigated by measuring the resistance at different temperatures and applied voltages. The changes in the crystal structure of the films at different temperatures were also explored using Raman measurements. The thermal diffusivity of the crystalline \(\hbox {V}_{2}\hbox {O}_{5}\) film was measured by the nanosecond thermoreflectance method. The microstructures of amorphous and crystalline \(\hbox {V}_{2}\hbox {O}_{5}\) were observed by SEM and XRD measurements. The temperature-dependent Raman spectra revealed that a structural phase transition does not occur in the crystalline film. The resistance measurements of an amorphous film indicated semiconducting behavior, whereas the resistance of the crystalline film revealed a substantial change near \(250\,{^{\circ }}\hbox {C}\), and Ohmic behavior was observed above \(380\,{^{\circ }}\hbox {C}\). This result was due to the metal–insulator transition induced by lattice distortion in the crystalline film, for which \(T_{\mathrm{c}}\) was \(260\,{^{\circ }}\hbox {C}\). \(T_{\mathrm{c}}\) of the film decreased from 260 \({^{\circ }}\hbox {C}\) to \(230\,{^{\circ }}\hbox {C}\) with increasing applied voltage from 0 V to 10 V. Furthermore, the thermal diffusivity of the crystalline film was \(1.67\times 10^{-7}\,\hbox {m}^{2}\cdot \hbox {s}^{-1}\) according to the nanosecond thermoreflectance measurements.     

Enhanced infrared transmission characteristics of microwave-sintered $$\hbox {Y}_{2}\hbox {O}_{3}$$–$$\hbox {MgO}$$MgO nanocomposite

Infrared (IR) transparent ceramics are found to have applications in demanding defence and space missions. In this work, \(\hbox {Y}_{2}\hbox {O}_{3}\)–\(\hbox {MgO}\) nanocomposites were synthesised by a modified single-step combustion technique. The characterisation of the as-prepared powder by X-ray diffraction and transmission electron microscopy revealed the presence of cubic phases of ultra-fine nanostructured \(\hbox {Y}_{2}\hbox {O}_{3 }\) and MgO, with an average crystallite size of \({\sim }19 \hbox { nm}\). For the first time the resistive and microwave heatings were effectively coupled for sintering the sample, and it was found that the sintering temperature and soaking time were reduced considerably. The pellets were sintered to 99.2% of the theoretical density at \(1430{^{\circ }}\hbox {C}\) for a soaking duration of 20 min. The well-sintered pellets with an average grain size of \({\sim }200 \hbox { nm}\) showed better transmittance properties relative to pure yttria. The promising percentage transmission of 80% in the UV–visible region and 82% in the mid-IR region shown by \(\hbox {Y}_{2}\hbox {O}_{3}\)–\(\hbox {MgO}\) nanocomposites can be tailored and made cost-effective to fabricate high-quality IR windows for strategic defence and space missions.     

Emission of Gas and $$\hbox {Al}_{2}\hbox {O}_{3}$$ Smoke in Gas–Al Particle Deflagration: Experiments and Emission Modeling for Explosive Fireballs

Emission of gas and \(\hbox {Al}_{2}\hbox {O}_{3}\) smoke within the deflagration of \(\hbox {H}_{2}{-}\hbox {O}_{2}\)–{\(\hbox {N}_{2}{-}\hbox {CO}_{2}\)}–Al particles has been studied in a closed combustion chamber at pressures of up to 18 bar and at gas temperatures of up to 3700 K. Measurements of radiance intensity were taken using a five wavelength pyrometer (0.660 \(\upmu \hbox {m}\), 0.850 \(\upmu \hbox {m}\), 1.083 \(\upmu \hbox {m}\), 1.260 \(\upmu \hbox {m}\), 1.481 \(\upmu \hbox {m}\)) and a grating spectrometer in the range (4.10 \(\upmu \hbox {m}\) to 4.30 \(\upmu \hbox {m}\)). In order to characterize the aluminum oxide smoke size and temperature, an inversion method has been developed based on the radiation transfer equation and using pyrometer measurements and thermochemical calculations of \(\hbox {Al}_{2}\hbox {O}_{3}\) smoke volume fractions. Temperatures in combustion gas have been determined using a method based on the assumed blackbody head of the 4.26 \(\upmu \hbox {m}\) \(\hbox {CO}_{2}\) emission line and on its spectral shift with pressure and temperature. For validation purpose, this method has been applied to measurements obtained when calibrated alumina particles are injected in a combustion chamber prior to gaseous deflagrations. This mathematical inversion method was developed to investigate explosive fireballs.     

Wettability of \hbox{R}(01\bar{1}2) single crystalline and polycrystalline \alpha\hbox{-}\hbox{Al}_{2}\hbox{O}_{3} substrates by Al–Si alloys over wide composition and temperature ranges

The wetting behaviors of $\hbox{R}(01\bar{1}2)$ single crystalline and polycrystalline $\alpha\hbox{-}\hbox{Al}_{2}\hbox{O}_{3}$ substrates by Al–Si alloys were studied over wide composition and temperature ranges. The wettability is quite good for all compositions of the alloys. The effect of temperature is moderate while that of the composition is significant. The dependence of the wettability on the alloy composition displays a “valley” profile with the minimum value appearing in the range of 60–70at.%Si. The wetting improvement by the addition of Al to Si mainly results from the decrease in the solid–liquid interfacial free energy by the Al segregation at the interface, while that by the addition of Si to Al results from the decrease in the surface tension of the liquid by the Si segregation.     

Ab Initio Study of Structural,Electronic, and Magnetic Properties of $\mathrm {A}_{1-x}^{\text {III}}$MnxBVI: In1−xMnxS-Diluted Magnetic Semiconductor

First-principles density functional calculations on the new class of diluted magnetic semiconductor \(A_{1-x}^{III}{Mn}_{x}B^{VI}\) In_1?x Mn _x S for x =?0.25 and 0.5 are investigated to study the structural, electronic, and magnetic properties, employing the full-potential linearized augmented plane wave method. Electronic band structures and density of states revealed a half-metallic character of In_1?x Mn _x S and show the stability of anti-ferromagnetic states as compared with ferromagnetic states. The calculated exchange constants J _dd are in good agreement with experimental and theoretical results on magnetic properties of single crystalline \(\mathrm {A}_{1-x}^{\text {III}}{\text {Mn}}_{x}\mathrm {B}^{\text {VI}}\) in the anti-ferromagnetic case. Our predicated calculations on the s,p-d exchange constants N ₀ α and N ₀ β show that they are lower than in \(\mathrm {A}_{1-x}^{\text {II}}{\text {Mn}}_{x}\mathrm {B}^{\text {VI}}\) DMS. The local environment is found tetrahedral as in the II–VI DMS and other (III,Mn) VI compounds. The total magnetic moment for In_1?x Mn _x S for different concentrations is in accordance with the exact value 5 μ _B and comes mainly from impurity Mn. The local magnetic moments of Mn ions are reduced from their free space charges values due to the p-d hybridization which produces small magnetic moments on the nonmagnetic In and S sites. The Curie temperature of In_1?x Mn _x S is calculated within the mean field approximation and compared with other DMS systems.     

Mathematical model of Boltzmann’s sigmoidal equation applicable to the set-up of the RF-magnetron co-sputtering in thin films deposition of $$\hbox {Ba}_{{x}}\hbox {Sr}_{1-{x}} \hbox {TiO}_{3}$$

In this work, we present the stoichiometric behaviour of \(\hbox {Ba}^{2+}\) and \(\hbox {Sr}^{2+}\) when they are deposited to make a solid solution of barium strontium titanate. \(\hbox {Ba}_{{x}}\hbox {Sr}_{1-{x}} \hbox {TiO}_{3}\) (BST) thin films of nanometric order on a quartz substrate were obtained by means of in-situ RF-magnetron co-sputtering at 495\({^{\circ }}\)C temperature, applying a total power of 120 W divided into intervals of 15 W that was distributed between two magnetron sputtering cathodes containing targets of \(\hbox {BaTiO}_{3}\) and \(\hbox {SrTiO}_{3}\), as follows: 0–120, 15–105, 30–90, 45–75, 60–60, 75–45, 90–30, 105–15 and 120–0 W. Boltzmann’s sigmoidal modified equation (Boltzmann’s profile) is proposed to explain the behaviour and the deposition ratio Ba/Sr of the BST as a function of the RF-magnetron power. The Boltzmann’s profile proposal shows concordance with experimental data of deposits of BST on substrates of nichrome under the same experimental conditions, showing differences in the ratio Ba/Sr of the BST due to the influence of the substrate.     

Solidification of NaCl–LiF–$$\hbox {CaF}_{2}$$ ternary composites

The purpose of this work is to refine the microstructure of eutectic halides, candidates to polaritonic metamaterials, through the directional solidification of ternary compositions. NaCl–LiF–\(\hbox {CaF}_{2}\) ternary composites have been solidified using Bridgman and micro-pulling-down techniques at pulling rates from 3 to 300 mm/h for the first time. The interparticle spacing is 12% smaller for this composition than for the binary fibrous NaCl–LiF eutectic. Conditions for solidification and growth in order to generate ternary aligned microstructures are discussed. The very small amount of melt remaining in the mixtures until \(580\,^{\circ }\hbox {C}\) is probably the consequence of solid solubility of LiCl in NaCl and the formation of the reciprocal salt pairs, as in NaCl–LiF. However, it does not prevent the solidification of homogenous ternary microstructures.     

Microstructure and microwave properties of {CaT{i}O}<Subscript>3</Subscript>–LaGaO<Subscript>3</Subscript> {solid solutions}

The phase assemblage, microstructure and microwave (MW) properties of xCaTiO₃-(1-x)LaGaO₃ (CT-LG) ceramics prepared by solid state synthesis from raw oxides and carbonates have been investigated. LG was predominantly single phase perovskite with space group, Pnma, but a small quantity of pyrochlore structured La₂Zr₂O₇ second phase was present due to the contamination from the ZrO₂ milling media. At MW frequencies, the temperature coefficient of resonant frequency (τ_{f}) of LG was --80~ppm/\({\circ}\)C, its permittivity, \(\varepsilon_{r} {=} \)27 and MW quality factor, \(Q^{*}f_{o} {=} \)97,000 (@5~GHz). As CT concentration increased, \(\tau_{f}\) and \(\varepsilon_{r}\) increased to The phase assemblage, microstructure and microwave (MW) properties of xCaTiO₃-(1-x)LaGaO₃ (CT-LG) ceramics prepared by solid state synthesis from raw oxides and carbonates have been investigated. LG was predominantly single phase perovskite with space group, Pnma, but a small quantity of pyrochlore structured La₂Zr₂O₇ second phase was present due to the contamination from the ZrO₂ milling media. At MW frequencies, the temperature coefficient of resonant frequency (τ_{f}) of LG was --80~ppm/ C, its permittivity, 27 and MW quality factor, 97,000 (@5~GHz). As CT concentration increased, and increased to $+$850~ppm/ C and 160, respectively but decreased to 20,000. Zero was achieved at 0.65 with 47, and 40,000, properties comparable with commercial compositions. However, for 0.5, a different second phase was observed which was rich in Ca and Ga. Electron diffraction patterns could be indexed according to a body centred cubic lattice, 12.5 ?. It is suggested that the presence of second phases in the CT-LG compounds may, in part, be responsible for the deterioration in .     

Photoacoustic Spectroscopic Study of Optical Properties of $$\hbox {Cu}_{2}\hbox {GeTe}_{3}$$ in Temperature Range from 80 K to 300 K

We used photoacoustic spectroscopy to investigate the optical properties of \(\hbox {Cu}_{2}\hbox {GeTe}_{3}\). The temperature dependence of the bandgap energy was evaluated from optical absorption spectra obtained in the photon energy range of 0.76 eV to 0.81 eV between 80 K and 300 K. We used the empirical and semi-empirical models of Varshni, Viña, and Pässler to describe the observed bandgap shrinkage in this compound. The Debye temperature and effective phonon temperature of the compound were estimated to be approximately 227.4 K and 151.6 K, respectively. Thus, the temperature dependence of the bandgap is mediated by acoustic phonons.     

Effect of the method for producing $$\hbox {}$$–$$\hbox {Cr}_{3}\hbox {C}_{2}$$Cr3C2 bulk composites on the structure and properties

Copper–chromium carbide composites containing a carbide phase of 20–30 vol% were obtained with the use of solid- and liquid-phase mechanosyntheses, followed by magnetic pulse compaction (MPC) and spark plasma sintering. The morphology, structural-phase composition, density, hardness and electrical conductivity of the composites were investigated. The structure of composites obtained by MPC represents regions of copper matrix hardened by superfine carbide precipitates surrounded by a layer of chromium carbide. In the composites obtained by spark plasma sintering, the copper matrix hardened by superfine carbide precipitates was divided into areas surrounded by a copper–chromium layer. A composite obtained by the MPC of the powders synthesized using solid-phase mechanosynthesis (MS) (copper, chromium and graphite) had the highest values of Vickers microhardness (4.6 GPa) and Rockwell hardness (HRA 69). The best value of electrical conductivity (36% IACS) was achieved using liquid-phase MS (copper, chromium and xylene) and spark plasma sintering. Liquid-phase MS is the only way to synthesize the powder with a small amount of the carbide phase and without contamination.