Improved microwave dielectric properties of La(Mg0.5Sn0.5)O3 ceramic with Ba2+ substitution

The microwave dielectric properties of La(Mg_0.5?xBa_xSn_0.5)O₃ ceramics were examined with a view to their exploitation for wireless communications. The La(Mg_0.5?xBa_xSn_0.5)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The La(Mg_0.5?xBa_xSn_0.5)O₃ ceramics contained La₂Sn₂O₇. An apparent density of 6.54 g/cm³, a dielectric constant ( $ \varepsilon_{r} $ ε r ) of 20.1, a quality factor (Q  $ \times $ ×  f) of 51,600 GHz, and a temperature coefficient of resonant frequency ( $ \tau_{f} $ τ f ) of ?82 ppm/°C were obtained for La(Mg_0.43Ba_0.07Sn_0.5)O₃ ceramics that were sintered at 1,550 °C for 4 h.     

Temperature-dependent electrical properties of 0.5Pb(Ni1/3Nb2/3)O3–(0.5 − x)PbTiO3–xPbZrO3 piezoceramics near the morphotropic phase boundary

0.5Pb(Ni_1/3Nb_2/3)O₃–(0.5 ? x)PbTiO₃–xPbZrO₃ (x = 0.10–0.20) polycrystalline ceramics were fabricated by solid-state reaction method. The phase structures, microstructure and temperature dependence of the electrical properties were investigated in detail. Both X-ray diffraction and Raman spectroscopy results indicated that the morphotropic phase boundary (MPB) separating tetragonal from rhombohedral phases located around the region with x = 0.14–0.16. Well-saturated ferroelectric P–E loops were obtained for all compositions and the compositions near MPB possessed the relative large remnant polarization P _r  ~ 24 μC/cm² and low coercive field E _c  ~ 5 kV/cm. High performance of electric-induced-strain property with $ d_{33}^{*} $ (S _max /E _max ) up to 1,140 pm/V could be achieved in the composition with x = 0.15. When the content of PbZrO₃ was 14 mol%, the ceramics showed slightly lowered piezoelectric coefficient $ d_{33}^{*} $ of 898 pm/V. But excellent temperature stability of piezoelectric property was exhibited that the $ d_{33}^{*} $ changed <10 % when the temperature increased from room temperature to 120 °C. The piezoelectric property of this solid solution makes it promising for application in multilayer piezoactuators.     

Influence of Ba2+ substitution on the microwave dielectric properties of Nd(Mg0.5Sn0.5)O3 ceramics

The microwave dielectric properties of Nd(Mg_0.5?xBa_xSn_0.5)O₃ ceramics were examined with a view to their exploitation in mobile communication. The Nd(Mg_0.5?xBa_xSn_0.5)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the Nd(Mg_0.47Ba_0.03Sn_0.5)O₃ ceramics revealed no significant variation of phase with sintering temperatures. A density of 6.91 g/cm³, a dielectric constant (ε _r ) of 19.14, a quality factor (Q × f) of 97,500 GHz, and a temperature coefficient of resonant frequency (τ _f ) of ?65.4 ppm/°C were obtained for Nd(Mg_0.47Ba_0.03Sn_0.5)O₃ ceramics that were sintered at 1,600 °C for 4 h.     

Dislocation structures in a { \bar{1} 104}/��11 \bar{2} 0�� low-angle tilt grain boundary of alumina (��-Al2O3)

An alumina (??-Al₂O₃) bicrystal with a ( $ \bar{1} $ 104)/[11 $ \bar{2} $ 0] 2^o low-angle tilt grain boundary was fabricated by diffusion bonding at 1500 °C in air, and the grain boundary was observed by transmission electron microscopy (TEM). High-resolution TEM observations revealed that the grain boundary consists of at least two kinds of dislocations. One is a perfect dislocation which has a Burgers vector of 1/3[ $ \bar{1} $ 2 $ \bar{1} $ 0]. The other is dissociated into two partial dislocations with a stacking fault on the (0001) plane, and each partial dislocation has a 1/6[ $ \bar{1} $ 101] edge component. It is suggested from structural considerations that the dissociated-dislocation pair originates from a b = 1/3[02 $ \bar{2} $ 1] perfect dislocation (i.e., 1/3[02 $ \bar{2} $ 1] ?? 1/6[02 $ \bar{2} $ 1] + 1/6[02 $ \bar{2} $ 1]). This dissociation produces a stacking fault in the anion sublattice. The stacking fault energy is estimated to be roughly 1.3 Jm^?2 based on the elastic theory. The authors discuss the dislocation structures and the stacking fault formed on the (0001) plane in detail.     

Nb Substituted Cu0.5Tl0.5Ba2(Ca3Nb1)Cu5O_{14-\delta} and Cu0.5Tl0.5Ba2(Ca4Nb1)Cu6O_{16-\delta} Superconductors

The effects of higher electro-negativity Nb substitution on the Ca site in Cu_0.5Tl_0.5Ba₂ (Ca₃Nb₁)Cu₅O $_{14-\delta}$ and Cu_0.5Tl_0.5Ba₂(Ca₄Nb₁)Cu₆O $_{16-\delta}$ superconductors have been investigated. The Nb doping has been found to increase the oxygen contents in Cu_0.5Tl_0.5Ba₂O $_{16-\delta}$ charge reservoir layer of the final compound. The post-annealing in the N₂ atmosphere has been found to improve the superconducting properties; however, O₂ annealing produced the material with inferior superconducting properties. The quantity of diamagnetism is increased with post-annealing in the nitrogen atmosphere; as N₂ annealing helps in the formation of material with optimum carriers concentration in the CuO₂ planes, which is done by the change in the charge state of thallium from Tl³⁺ to Tl¹⁺. The Nb substitution has been found to develop the higher CuO₂ planner phases such as Cu_0.5Tl_0.5Ba₂Can _?2Nb₁Cun ₂ n+4?δ (n=5,6) with enhanced T _c's.     

Structural properties of Cd–Co ferrites

Ferrite samples with composition, Cd $_{\emph{x}}$ Co $_{1-\emph{x}}$ Fe₂O₄ (x = 0·80, 0·85, 0·90, 0·95 and 1·0), were prepared by standard ceramic method and characterized by XRD, IR and SEM techniques. X-ray analysis confirms the formation of single phase cubic spinel structure. Lattice constant and grain size of the samples increase with increase in cadmium content. Bond length (A–O) and ionic radii ( ${\emph{r}}_{\rm {A}})$ on A-sites increase, whereas bond length (B–O) and ionic radii ( ${\emph{r}}_{\rm{B}})$ on B-site decrease. The crystallite sites of the samples lie in the range of 29·1–42·8 nm. IR study shows two absorption bands around 400 cm^???1 and 600 cm^???1 corresponding to tetrahedral and octahedral sites, respectively.     

Correlation between crystal structures and vibration modes of Ba[(Zn1−x Mg x )1/3Nb2/3]O3 ceramics as a function of sintering temperatures

Ba[(Zn_1?x Mg _x )_1/3Nb_2/3]O₃ (short for BZMN, x = 0.4, 0.6, 0.8) solid solution ceramics were sintered by conventional solid-state sintering technique at different temperatures. Effects of sintering temperatures on phonon modes and crystal structures of BZMN ceramics were investigated by X-ray diffraction and vibration spectra (Raman spectroscopy as well as Fourier transform far-infrared reflection spectroscopy) techniques. The results reveal that sintering temperatures have an obviously influence on phonon modes, which are closely related to the 1:2 ordered structures. For the samples where x = 0.4, they possess the cubic structure (Pm3m), and the ordering degree decreases with the increase in the temperature. For the samples where x = 0.6, phase transition occurs after sintered at 1,500 °C, i.e., a 1:2 ordered monoclinic unit cell is formed. For the samples where x = 0.8, they possess the hexagonal structures ( $P\bar{3}m1$ ), and the ordering degree increases with the increase in the temperatures.     

Features in the formation of Ge/Si multilayer nanostructures under ion-beam-assisted crystallization

A method of combined ion-beam crystallization of the Ge/Si multilayer nanostructures is proposed. Using atomic-force microscopy and electron microscopy, we observed the formation of an array of germanium quantum dots with lateral dimensions 〈a〉 = 12–15 nm at the following conditions: silicon-substrate temperature T = 330–350°C, ion-beam energies E _Ge + = 30–40 eV, $E_{Ar^ + }^0 = 230 - 240$ eV (primary pulsed defect formation mode), $E_{Ar^ + } = 130 - 140$ eV (permanent diffusion stimulation mode), and ion-beam fluences $f_{Ge^ + } = 1.5 \times 10^{14} cm^{ - 2} s^{ - 1} $ , $f_{Ar^ + } = 5 \times 10^{12} cm^{ - 2} s^{ - 1} $ . The Raman spectroscopy data indicate the experimental possibility of low-temperature ion-stimulated growth of the spacer layers of silicon (T = 420–450°C, $E_{Ar^ + } = 80 - 90$ eV, $E_{Si^ + } = 30 - 40$ eV, $f_{Si^ + } = 3.5 \times 10^{14} cm^{ - 2} s^{ - 1} $ ) and the formation of multilayer structures with Ge _x Si_{1 ? x} quantum dots (x > 0.85).     

Theoretical Investigations on Electrocaloric Properties of \mathrm{PbZr}_{0.95}\mathrm{Ti}_{0.05}\mathrm{O}_{3} Thin Film

Based on a phenomenological model, the electrocaloric effect (ECE) accompanied with the ferroelectric-to-paraelectric phase transition in a PbZr $_{0.95}$ 0.95 Ti $_{0.05}$ 0.05 O $_{3}$ 3 thin film was investigated. The extracted data reveal many features of the ECE such as electrocaloric entropy changes, heat capacity changes, and temperature changes as functions of temperature due to different electric fields shifts. From the behavior of the PbZr $_{0.95}$ 0.95 Ti $_{0.05}$ 0.05 O $_{3}$ 3 thin film in phase transitions, it leads to a large change of heat capacity of 105.94 J  ${\cdot }\,$ · kg ${^{-1}}\,{\cdot }\,{^{\circ }}$ ? 1 · ° C, a temperature change of 22.44 K, and a relative cooling power of 1469 J  ${\cdot }$ ·  kg $^{-1}$ ? 1 .     

Behaviour of LaAlO3+LnTiTaO6 (Ln= Ce, Pr or Nd) dielectric ceramic mixtures

The 0·1LaAlO₃+0·9LnTiTaO₆ (Ln= Ce, Pr or Nd) ceramics are prepared through solid state ceramic route. The structure of the materials is studied using X-ray diffraction analysis. The microstructure is analysed using scanning electron microscopy. The dielectric properties in the radio as well as in the microwave frequencies are measured and discussed. The photoluminescence of a representative sample is also analysed. The dielectric constant ( $\varepsilon_{r})$ and temperature coefficient of resonant frequency ( $\tau_{f})$ are tailored without appreciable change in the quality factor. The measured values of $\varepsilon_{r}$ and $\tau _{f}$ are compared with the corresponding predicted values. These mixtures can be made useful in optical and microwave communication.     

Temperature Response of BaZrO3-Inclusion to YBa2Cu3O7−δ Probed by Magneto-Transport Measurements

This paper reflects a simple and practically scalable technique, in which attempts have been made for preparation of fine BaZrO₃ (BZO) as defects in YBa₂Cu₃O_7?δ (YBCO) superconductor, to enhance superconducting properties. The texture growth of YBCO + xBZO (x=1.0,2.5,5.0 and 10.0 wt.%) composites has been made through solid-state reaction route by employing calcined YBCO and sub-micron sized powders of BZO. The phase formation, texture and grain alignment were analyzed using XRD and SEM. The magnetoresistivity data obtained as a function of temperature (T) in the tail region shows two key features: first an anomalous secondary peak at $T_{c_{\mathrm{on}2}}$ well below 92 K as a function of BZO content with varying magnetic fields, and secondly a drop in global resistivity transition temperature (T _c0) following the incorporation of excess BZO to the grain boundaries. Impurities appear to reduce $T_{c_{\mathrm{on}2}}$ greatly to the lower-temperature values as a function of BZO content and to influence the onset of $T_{c_{\mathrm{on}1}}$ in presence of varying magnetic fields. The findings of this investigation suggest the presence of multiple transition temperatures in the composites.     

Rational formulas for traces in zero-dimensional algebras

We present a rational expression for the trace of the multiplication map Times _r : A → A in a finite-dimensional algebra ${A := \mathbb {K}[x_1,\ldots,x_n] /\mathcal {I}}$ in terms of the generalized Chow form of ${\mathcal{I}}$ . Here, ${\mathcal{I} \subset \mathbb {K}[x_1,\ldots,x_n]}$ is a zero-dimensional ideal, ${\mathbb {K}}$ is a field of characteristic zero, and r(x ₁,..., x _n ) a rational function whose denominator is not a zero divisor in A. If ${\mathcal {I}}$ is a complete intersection in the torus, we get numerator and denominator formulas for traces in terms of sparse resultants.     

Dielectric,ferroelectric, and field-induced strain properties of Ta-doped 0.99Bi0.5(Na0.82K0.18)0.5TiO3–0.01LiSbO3 ceramics

Ta-doped 0.99Bi_0.5(Na_0.82K_0.18)_0.5TiO₃–0.01LiSbO₃ (BNKTT–LS) ceramics were prepared through a conventional mixed oxide solid-state sintering route. Partial substitution of Ta for Ti decreased the dielectric constant and depolarization temperature. The dielectric curves, polarization and strain hysteresis loops demonstrated that the incorporation of Ta stabilized the canonical relaxor phase of BNKT–LS ceramics leading to the degradation of piezoelectric and ferroelectric responses. The destabilization of field-induced ferroelectric order at x = 0.013 was accompanied by substantial enhancement in strain level. A unipolar field-induced strain of 0.39 % with a normalized strain (S _max/E _max =  $ d_{33}^{*} $ ) of 650 pm/V was achieved at a driving field of 6 kV/mm. The observed large strain can be attributed to the non-ergodic relaxor phase at zero electric field that transformed into an ergodic relaxor phase under the influence of the applied electric field.     

The Splitting of SDW State into Commensurable and Incommensurables Ones and the Peculiarities of the Behavior of Thermodynamic Quantities in a Magnetic Field Arbitrarily Oriented to Magnetization in Quasi Two-Dimensional Systems

The quasi-two-dimensional system in which magnetism is caused by spin density wave (SDW) with an anisotropic energy spectrum (with defined impurity concentration x) is examined. The wave vector $\vec{Q}$ is supposed to be different from 2k _F and the umklapp scattering (U-processes) is taken into account. The system is placed in a magnetic field arbitrarily oriented with respect to the vector $\vec{M}_{Q}$ . The basic equations for order parameters $M_{Q}^{z}, M_{Q}', M_{z}, M^{\sigma}$ are obtained and the system of these equations is transformed taking into account the U-processes. The particular cases $( \tilde{H} \Vert \vec{M}_{Q} )$ and $( \tilde{H} \bot \vec{M}_{Q} )$ and the case of small arbitrarily oriented magnetic fields $\vec{\tilde{H}}$ are examined in detail. The conditions of the system transition to commensurable and incommensurable SDW state are analyzed. The phase diagram (T,x) at H=0 is traced. The influence of the magnetic field $\vec{\tilde{H}}$ on the temperature of magnetic transition is researched and the aspect of the phase diagram in magnetic field in the cases H ^z H ^σ =0 is presented. The longitudinal magnetic susceptibility χ _∥ which demonstrates that at x<x _c the temperature behavior is similar to the case when the system has a gap, and at x>x _c to a gapless case. At x～x _c in the dependence X _∥(T) a local maximum appears. The influence of the energy spectrum anisotropy on the system’s properties is researched. Also the angular anisotropy of the quantity χ _∥ at different values of T and x is determined.     

Effect of Sm substitution on microwave dielectric properties of Nd(Mg0.5Sn0.5)O3 ceramics

The microwave dielectric properties of Nd_(1?x)Sm_x(Mg_0.5Sn_0.5)O₃ ceramics were examined with a view to their exploitation in mobile communication. The Nd_(1?x)Sm_x(Mg_0.5Sn_0.5)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the Nd_0.98Sm_0.02(Mg_0.5Sn_0.5)O₃ ceramics revealed no significant variation of phase with sintering temperatures. A density of 6.87 g/cm³, a dielectric constant (ε _r ) of 19.2, a quality factor (Q × f) of 104,300 GHz, and a temperature coefficient of resonant frequency (τ _f ) of ?57 ppm/°C were obtained for Nd_0.98Sm_0.02(Mg_0.5Sn_0.5)O₃ ceramics that were sintered at 1,550 °C for 4 h.     

Enhancing the microwave dielectric properties of Nd (Mg0.5Sn0.5)O3 ceramics by substituting Nd3+ with Ca2+

The microwave dielectric properties of Nd_(1?2x/3)Ca_x(Mg_0.5Sn_0.5)O₃ ceramics were examined to evaluate their exploitation for mobile communication. Nd_(1?2x/3)Ca_x(Mg_0.5Sn_0.5)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the Nd_2.9/3Ca_0.05(Mg_0.5Sn_0.5)O₃ ceramics revealed no significant variation of phase with the sintering temperature. Nd_2.9/3Ca_0.05(Mg_0.5Sn_0.5)O₃ ceramics that were sintered at 1,550 °C for 4 h had the following properties: a density of 6.86 g/cm³, a dielectric constant (ε_r) of 19.3, a quality factor (Q × f) of 99,000 GHz, and a temperature coefficient of resonant frequency (τ _f ) of ?65 ppm/°C.     

Magnetocaloric Effect in Half-Metallic Double Perovskite Sr_{0.4}Ba_{1.6-x}Sr_{x}FeMoO_{6}

The magnetocaloric effect in half-metallic double perovskite Sr $_{0.4}$ Ba $_{1.6-x}$ Sr $_{x}$ FeMoO $_{6}$ (x = 0, 0.2, 0.4, 0.6) was investigated. It is shown that Sr $_{0.4}$ Ba $_{1.6-x}$ Sr $_{x}$ FeMoO $_{6}$ exhibits a magnetic entropy change of 0.078 J $\,\cdot \, $ kg $^{-1}\,\cdot \, $ K $^{-1}$ upon 0.2 T magnetic field variation. Through these results, polycrystalline samples of Sr $_{0.4}$ Ba $_{1.6-x}$ Sr $_{x}$ FeMoO $_{6 }$ have some potential applications for magnetic refrigerants over a wide-temperature range, including room temperature.     

Determination of thermodynamic interactions of poly(l-lactide) and biphasic calcium phosphate/poly(l-lactide) composite by inverse gas chromatography at infinite dilution

Inverse gas chromatography at infinite dilution was applied to determine the thermodynamic interactions of poly(l-lactide) (PLLA) and the composite of biphasic calcium phosphate and PLLA (BCP/PLLA). The specific retention volumes, $ V_{\text{g}}^{0} $ , of 11 organic compounds of different chemical nature and polarity (non-polar, donor or acceptor) were determined in the temperature range of 308–378 K for PLLA and 308–398 K for BCP/PLLA. The weight fraction activity coefficients of test sorbates, $ \Omega_{1}^{\infty } $ , and the Flory–Huggins interaction parameters, $ \chi_{12}^{\infty } $ , were estimated and discussed in terms of interactions of the sorbates with PLLA and BCP/PLLA. Also, the partial molar free energy, $ \Delta G_{1}^{\infty } $ , the partial molar heat of mixing, $ \Delta H_{1}^{\infty } $ , the sorption molar free energy, $ \Delta G_{1}^{\text{S}} $ , the sorption enthalpy, $ \Delta H_{1}^{\text{S}} $ , and the sorption entropy, $ \Delta S_{1}^{\text{S}} $ , were analyzed. A different chromatographic behavior of the two investigated samples, PLLA and BCP/PLLA, was observed. The values of $ \Omega_{1}^{\infty } $ indicated n-alkanes, diethyl ether, tetrahydrofurane (THF), cyclohexane, benzene, dioxane (except for 338 K), and ethyl acetate (EtAc) (except for 338 K) as non-solvents, and chloroform (CHCl₃) as good solvent (except for 378 K) for PLLA. For BCP/PLLA, CHCl₃, EtAc (for 378 K), dioxane (except for 378 K), and THF were indicated as good solvents.     

Molecular beam epitaxy of semipolar AlN(11\bar{2}2) and GaN(11\bar{2}2) on m-sapphire

We report on the plasma-assisted molecular-beam epitaxy of semipolar $\hbox{AlN}(11\bar{2}2)$ and GaN( $11\bar{2}2$ ) films on $(1\bar{1}00)$ m-plane sapphire. AlN deposited on m-sapphire settles into two main crystalline orientation domains, $\hbox{AlN}(11\bar{2}2)$ and $\hbox{AlN}(10\bar{1}0),$ whose ratio depends on the III/V ratio. Growth under moderate nitrogen-rich conditions enables to isolate the $(11\bar{2}2)$ orientation. The in-plane epitaxial relationships of $\hbox{AlN}(11\bar{2}2)$ on m-plane sapphire are $[11\bar{2}\bar{3}]_{\rm AlN} \vert \vert [0001]_{\rm sapphire}$ and $[1\bar{1}00]_{\rm AlN} \vert \vert [11\bar{2}0]_{\rm sapphire}.$ GaN deposited directly on m-sapphire results in ( $11\bar{2}2$ )-oriented layers with ( $10\bar{1}\bar{3}$ )-oriented inclusions. A ～100 nm-thick AlN( $11\bar{2}2$ ) buffer imposes the ( $11\bar{2}2$ )-orientation for the GaN layer grown on top. By studying the Ga-desorption on GaN( $11\bar{2}2$ ), we conclude that these optimal growth conditions corresponds to a Ga excess of one monolayer on the GaN( $11\bar{2}2$ ) surface.     

Ba3(P1 − x Mn x O4)2 : Blue/green inorganic materials based on tetrahedral Mn(V)

We describe a blue/green inorganic material, Ba₃(P_1???x Mn _x O₄)₂ (I) based on tetrahedral MnO $_{4}^{3-}$ :3d ²chromophore. The solid solutions (I) which are sky-blue and turquoise-blue for x ≤ 0·25 and dark green for x ≥ 0·50, are readily synthesized in air from commonly available starting materials, stabilizing the MnO $_{4}^{3-}$ chromophore in an isostructural phosphate host. We suggest that the covalency/ionicity of P–O/Mn–O bonds in the solid solutions tunes the crystal field strength around Mn(V) such that a blue colour results for materials with small values of x. The material could serve as a nontoxic blue/green inorganic pigment.