Effects of ZnO on the piezoelectric properties of Pb(Mn1/3Sb2/3)O3-Pb(Zr,Ti)O3 ceramics

Perovskite-type 0.05 Pb(Mn_1/3Sb_2/3)O₃-0.95 Pb(Zr_0.5Ti_0.5)O₃ (PMS-PZT) was synthesized by conventional bulk ceramic processing technique. ZnO as a dopant up to 0.5 mol% was incorporated into the PMS-PZT system, and the effects on piezoelectric properties were investigated. Pyrochlore phase was not detected to form during the synthesis of the PMS-PZT system with 0∼0.5 mol% ZnO addition. The highest density of 7.92 g/cm³ was obtained when sintered at 1200°C for 2 hrs. Piezoelectric properties as a function of ZnO content were evaluated using a gain phase analyzer. Piezoelectric charge constant (d₃₁) and piezoelectric voltage output coefficient (g₃₁) increased up to −130 pC/N and −24.9 × 10³Vm/N, respectively, with increasing ZnO content. Mechanical quality factor (Q _m) was shown to reduce considerably with increasing ZnO content. When 0.3 mol% of ZnO was added into the system, electromechanical coupling factor (k _p) and relative dielectric constant () reached to the maximum of 56% and 1,727, respectively.     

Oxygen permeability, stability and electrochemical behavior of \Pr _{2} {\text{NiO}}_{{4 + \delta }} -based materials

The high-temperature electronic and ionic transport properties, thermal expansion and stability of dense $ \Pr _{2} {\text{NiO}}_{{4 + \delta }} ,\Pr _{2} {\text{Ni}}_{{0.9}} {\text{Fe}}_{{0.1}} {\text{O}}_{{4 + \delta }} $ and $ \Pr _{2} {\text{Ni}}_{{0.8}} {\text{Cu}}_{{0.2}} {\text{O}}_{{4 + \delta }} $ ceramics have been appraised in comparison with K₂NiF₄-type lanthanum nickelate. Under oxidizing conditions, the extensive oxygen uptake at temperatures below 1073–1223 K leads to reversible decomposition of Pr₂NiO₄-based solid solutions into Ruddlesden–Popper type Pr₄Ni₃O₁₀ and praseodymium oxide phases. The substitution of nickel with copper decreases the oxygen content and phase transition temperature, whilst the incorporation of iron cations has opposite effects. Both types of doping tend to decrease stability in reducing atmospheres as estimated from the oxygen partial pressure dependencies of total conductivity and Seebeck coefficient. The steady-state oxygen permeability of $ \Pr _{2} {\text{NiO}}_{{4 + \delta }} $ ceramics at 1173–1223 K, limited by both surface-exchange kinetics and bulk ionic conduction, is similar to that of $ {\text{La}}_{2} {\text{NiO}}_{{4 + \delta }} $ . The phase transformation on cooling results in considerably higher electronic conductivity and oxygen permeation, but is associated also with significant volume changes revealed by dilatometry. At 973–1073 K, porous $ \Pr _{2} {\text{Ni}}_{{0.8}} {\text{Cu}}_{{0.2}} {\text{O}}_{{4 + \delta }} $ electrodes deposited onto lanthanum gallate-based solid electrolyte exhibit lower anodic overpotentials compared to $ {\text{La}}_{2} {\text{Ni}}_{{0.8}} {\text{Cu}}_{{0.2}} {\text{O}}_{{4 + \delta }} $ , whilst cathodic reduction decreases their performance.     

Effects of the gas flow rate on the ionic conductivity of {\text{CaZr}}_{0.95} {\text{In}}_{0.05} {\text{O}}_{3 - \delta } ceramics

With coarse CaCO₃, nano ZrO₂ and In₂O₃ as raw materials, fine ${\text{CaZr}}_{0.95} {\text{In}}_{0.05} {\text{O}}_{3 - \delta } $ powders were synthesized at 1000°C by an optimized solid-state method. With the powders, ceramics with relative density as high as 98% were successfully fabricated at the temperature as low as 1400°C. The effects of gas flow rate on the conductivity of the ${\text{CaZr}}_{0.95} {\text{In}}_{0.05} {\text{O}}_{3 - \delta } $ ceramics under wet air conditions were first studied. The results showed that with the increase of temperature, the effects became more and more significant. In order to gain insight into the ion transfer mechanism of the electrolyte, the absorption and diffusion processes were analyzed. It was suggested that at lower temperature, the diffusion step was the rate-determining step. However, with the increase of the temperature, the adsorption process became the rate-determining step at lower flow rates.     

Transport Properties of the Mixed-Conducting SrFe1.2Co0.3Ox

Single phase SrFe_1.2Co_0.3O_x sample with layered crystal structure was prepared using a solid state reaction method. Electrical conductivity and apparent oxygen diffusion coefficients of the SrFe_1.2Co_0.3O_x sample were measured as functions of temperature in atmospheres of various oxygen partial pressures . Total and ionic conductivities were determined by using the conventional four-probe and electron blocking four-probe methods, respectively. The apparent oxygen diffusion coefficient was derived from the time-dependent conductivity relaxation data of the reequilibrium process after abruptly changing the in the surrounding atmosphere. Several atmospheres of different were established by the use of premixed gas cylinders. The conductivity of SrFe_1.2Co_0.3O_x increases with increasing temperature and . At 900°C in air, the total conductivity and ionic conductivity are 10 and 8S · cm^-2, respectively. The ionic transference number ( 0.8 in air) does not have strong temperature dependence. The activation energy increases with decreasing . In air, the activation energy has a low value of 0.37 eV. The apparent oxygen diffusion coefficient was at 950°C over a wide range of .     

A Novel Oxygen Sensor Based on a Metal–Metal Oxide Scale System

A novel oxygen sensor was proposed. The sensor, an electrochemical cell, was composed of a metal as reference electrode, its oxide scale as electrolyte and Pt or other adequate materials as sample electrode. It is expected that the electrolyte is self-restorative because it can be restored by high temperature oxidation. The emf measurements were carried out at 873 K in cells using zirconium. At atm, the emf vs. plot lies on a straight line and its gradient is 2.303RT/4F, suggesting t _ion=1 at the surface of the scale. The emf steeply decreases with decreasing at atm which can not be explained by the increase in the electronic conductivity and is explained by a gas laminar film phase at the surface of the sample electrode.     

Effects of Mg doping concentration on the band gap of ZnO/Mg x Zn1−x O multilayer thin films prepared using pulsed laser deposition method

Epitaxial ZnO/Mg _x Zn_1-x O multilayer thin films (x?=?0~0.15) were prepared on c-Al₂O₃ substrates by pulsed laser deposition and their crystallinity and optical properties were investigated using X-ray diffraction, TEM, and UV-Vis spectroscopy. ZnO/Mg _x Zn_1-x O multilayer thin films were grown by stacking alternate layers of ZnO and Mg _x Zn_1?x O with laser fluence of 3 J/cm², repetition rate of 5 Hz, substrate temperature of 600 °C, and oxygen partial pressure of 5?×?10^–4 Torr. The thickness of individual ZnO and Mg _x Zn_1?x O layers was maintained at 3 and 6 nm, respectively, and the total thickness of the films was kept in 300 nm. X-ray diffraction results showed that the multilayer thin films were grown epitaxially on c-Al₂O₃ substrates with an epitaxial orientation relationship of $\left. {\left( {0001} \right)\left[ {10\bar 11} \right]_{{\text{multilayer}}} } \right\|\left( {0001} \right)\left[ {10\bar 11} \right]_{{\text{Al}}_{\text{2}} {\text{O}}_{\text{3}} } $ . Cross-sectional TEM micrographs showed alternating layers of bright and dark contrast, indicating the formation of ZnO/Mg _x Zn_1?x O multilayer thin films. The 2θ value of Mg _x Zn_1?x O (0002) peak increased from 34.30° at x?=?0 to 34.67° at x?=?0.15 with increasing Mg doping concentration in the multilayer thin films. The absorption edge in the UV-Vis spectra shifted to shorter wavelength from 360 at x?=?0 to 342 nm at x?=?0.15 and the band gap energy increased from 3.27 eV at x?=?0 to 3.54 eV at x?=?0.15.     

Die Berechnung von Übergangsvorgängen bei Induktionsmaschinen mit Stromverdrängungsläufern

Übersicht Zur rechnerischen Untersuchung nichtstationärer Vorgänge bei Asynchronmaschinen mit Käfigläufern wird die Stromverdrängung mit Hilfe der Doppelkäfignäherung in einem auf der Grundlage der Zweiachsentheorie aufgebauten elektromechanischen Gleichungssystem berücksichtigt. Die Einflüsse der Eisensättigung in der Leerlaufkennlinie und in der Kurzschlußkennlinie können in erweiterten Gleichungen mit beachtet werden. Die Auswertung des Systems erfolgt in der Nachbildung am Analogrechner. Die Rechenergebnisse von Hochlauf-, Einschalt- und Netzumschaltungsuntersuchungen für große Motoren werden angegeben.

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Contents The behaviour of squirrel-cage induction machines is described by a system of differential equations based on the cross-field theory. With respect to the skin effect the rotor is represented by a double-cage approximation. Saturation of the main flux and leakage flux as well can be taken into account by an expanded form of equations. An analogue computer was used for numerical computation; results are given for the transient performance of large motors in cases of starting, starting with pony-motor and reclosing on an auxiliary power supply line.

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Übersicht der wichtigsten Formelzeichen

Indizes S Ständer - L Läufer allgemein - o Oberkäfig - u Unterkäfig - h Hauptfeld - a, b, c Dreiphasensystem - , , o Komponentensystem - N Nennwert - K Kurzschlußwert; Kippwert - auf Streuung bezogen - R Regulierläufer (Schleifringläufer) - G Gegenwirkung (Last) - A Anlauf - * konj. komplexer Wert Veränderliche Unabhängig =2f·t Zeitwinkel Abhängig u Spannungen - i Ströme - verkettete Flüsse - m Drehmoment - s Schlupf - _s Korrekturfaktor für Ständerwiderstand - Korrekturfaktor für Streuwegsättigung - Komplexe Zusammenfassung der ,-Komponenten u=u +ju ; +j i=i +ji Konstanten Kurzschlußreaktanzen - Kurzschlußdämpfungen - Kurzschlußströme - Nennflüsse Weitere Koeffizienten T _A mech. Anlaufzeitkonstante - Gewichtsfaktoren bei der Hauptflußbildung Im allgemeinen werden Veränderliche mit kleinen, konstante Wert mit großen Buchstaben bezeichnet.     

Improvement in microwave dielectric properties of Sr<Subscript>2</Subscript>TiO<Subscript>4</Subscript> ceramics through post-annealing treatment

Sr₂TiO₄ ceramics were synthesized via the conventional solid-state reaction process, and the effects of post-annealing treatment in air on the microwave dielectric properties and defect behavior of title compound were investigated systematically. The Q?×?f values could be effectively improved from 107,000 GHz to 120,300 GHz for the specimens treated at 1450 °C for 16 h. The thermally stimulated depolarization currents (TSDC) revealed two kinds of defect dipoles [\( \left({\mathrm{Ti}}_{\mathrm{Ti}}^{\hbox{'}}-{V}_{\mathrm{O}}^{\bullet \bullet}\right) \) and \( \left({V}_{\mathrm{Sr}}^{"}-{V}_{\mathrm{O}}^{\bullet \bullet}\right) \)] and oxygen vacancies \( \left({V}_{\mathrm{O}}^{\bullet \bullet}\right) \) were considered the main defects in Sr₂TiO₄. Under a post-annealing treatment in air, the concentrations of such defects in the ceramics decreased. Meanwhile, the impedance spectrum revealed the activation energy of the grain boundaries increased. These evidences could account for the improvement of Q?×?f values. Accompanied with a high ε_r of 40.4 and a large τ_f of 126 ppm/°C, the enhanced high-Q Sr₂TiO₄ ceramics can be good candidates for applications in wireless passive temperature sensing.     

Frequency-temperature compensation mechanism for bismuth based dielectric/PTFE microwave composites

The dielectric property and thermal expansion property of Bi₂O₃-ZnO-Nb₂O₃-based (BZN) ceramics filler reinforced composites have been investigated as a function of temperature range from ?50 to 175 °C. The composites with adjustable temperature coefficient of frequency (τ _f ) and dielectric temperature coefficient ( $ \alpha _{\varepsilon } $ ) are achieved by filling the ceramic filler with different $ \alpha _{\varepsilon } $ into polymer matrix. A series of polytetrafluoroethylene (PTFE) based composites blended with different amount of ceramic filler with different $ \alpha _{\varepsilon } $ have been studied in this paper. The results indicated that with the amount of ceramic filler increasing, both of the relative permittivity and dissipation factor of composites increased. Composite filled with positive $ \alpha _{\varepsilon } $ (245 ppm/°C) BZN ceramic filler (40 vol.%) has low $ \alpha _{\varepsilon } $ (22 ppm/°C), while filled with near-zero $ \alpha _{\varepsilon } $ (10 ppm/°C) BZN ceramic filler (40 vol.%) have low τ _f (?5 ppm/°C).     

Theorie der Raumladungs-Sperrschicht einer Niederdruckentladung zur Verwendung für eine Theorie der Rückzündung

Zusammenfassung Im ersten Teil der Arbeit wird die Theorie über die Raumladungs-Sperrschicht an der Grenze zwischen einem Niederdruck-Plasma und einer negativen Elektrode ausführlich dargestellt. Auf Grund des Boydschen Schichtkriteriums wird über die Ergebnisse von Bohm hinausgehend eine neue Randbedingung allgemein für die positive Säule im Bereich der ambipolaren Diffusion aufgestellt. Die Gültigkeit dieser Randbedingung wird an früheren Sondenmessungen von Klarfeld geprüft und bestätigt gefunden. Mittels der neuen Randbedingung wird in Verbindung mit früheren Messungen die Beweglichkeit der Quecksilber-Ionen bestimmt, die sich, bezogen aufp=1, als allein von der Elektronentemperatur abhängig erweist. Diese Ergebnisse werden bei der Betrachtung der Entionisierung des Gitter-Anodenraumes und des Ionenrückstromes zur Anode verwendet. Der Entionisierungsvorgang wird bei vereinfachter Anodensystemgeometrie sowohl statisch (mit Vernachlässigung der Sperrschicht vor der Anode) als auch dynamisch mit Berücksichtigung der Sperrschicht betrachtet. Es werden Meßergebnisse wiedergegeben und Übereinstimmung der Theorie mit der Erfahrung gefunden. Der von Koch angegebene Ansatz für den dynamischen Ionenrückstrom wird erweitert, womit die von Zipfel gemessenen hohen dynamischen Rückströme erklärt werden können. Es ergibt sich sowohl theoretisch als auch auf Grund einer dargestellten Sondenmeßmethode, daß die gemessenen Anodenrückströme bis zu sehr hohen Steilheiten der anlaufenden Sprungspannung (du /dt) praktisch reine Ionenströme sind.Übersicht der verwendeten Symbole A Konstante der Feldemissionsgleichung definiert durch Gl. (64) - a Korrekturgröße definiert durch Gl. (75) - B Konstante der Feldemissionsgleichung definiert durch Gl. (64) - b _i Beweglichkeit der Hg-Ionen;b _i1=b_ip - C wird mehrmals als Konstante verwendet - C ₁ - C ₂ - D Dimensionslose Größe, DurchschlagsbedingungD1 - D _a Ambipolare Diffusionskonstante für Hg,D _a1=D_a·p - d Abstand, Gitter-Anode - E Elektrische Feldstärke, an der AnodeE ₀, im Plasma an der Grenze zur SperrschichtE - e Elementarladung,e=1,602·10^–19 As - F _eff effektive Anodenoberfläche - J ₀,J ₁ Besselfunktion o. Ordnung und 1. Ordnung - i Anodenstrom - i _R Anodenrückstrom, ^: Spitzenwert, Index stat: statisch, Index dyn: dynamisch - j Stromdichte, ^: Spitzenwert, IndexV: Verschiebungsstromdichte - j ⁺ Ionenstromdichte zur Anode, ^: Spitzenwert. Bedeutung der Indizes:stat, statisch;dyn, dynamisch;K, Konvektion;P, vom Plasma;S, in der Sperrschicht erzeugt - j ⁺ Ionenwandstromdichte - j ^– Elektronenstromdichte, IndexF, in einem Feldemissionszentrum der Anode - k Boltzmann-Konstantek=1,38·10^–23 VAs/grad - l wird mehrmals als Längenmaß verwendet - M Masse eines Hg-IonsM=3,33·10^–25 kg - m Masse eines Elektronsm=9,106·10^–31 kg - m _F Feldverstärkungsfaktor Gl. (61) - n Neutralgasdichte; Index o, vor der Anode beit=0; Index 1, fürp=1,n ₁=3,54×10²² Atome je m³ und Torr - n _i, n_e Ionen- und Elektronendichte;n _e0, in der Symmetrie-Mitte des Plasmas;n _e, an der Plasmagrenze - p auf 0 °C reduzierter Druck,p=n/n ₁ - mittlerer Ionisierungsquerschnitt innerhalb der Schicht Gl. (71) - mittlerer Umladequerschnitt innerhalb der Schicht Gl. (79) - R Gefäßradius; Gitter- bzw. Blendenlochradius - r Zylinderkoordinate - S definiert durch Gl. (3) - T Zeitkonstante des gemessenen Rückstromes - T ₀ Zeitbereich für die Wahrscheinlichkeit Gl. (85) - T _A Temperatur der Anode - t Zeit - t Zeitdauer bis die Sperrschicht eine Sonde vor der Anode erreicht - U _e Elektronentemperatur, 11600 °K entsprechen 1 V - u Potential;u , Potentialdifferenz an der Sperrschichtu ^* , beim Spitzenwert des Rückstromesu _spr, Sprungspannung (Anode-Kathode) - u Anfangsgeschwindigkeit der Ionen an der Sperrschicht in Volt - Koordinate - - Korrekturgröße definiert durch Gl. (22) - Koeffizient der Elektronenemission durch auftreffende Ionen - Sperrschichtdicke, ₀ definiert durch Gl. (22) - ₀= 8.86 · 10^-12 As/Vm - - _i , definiert in Gl. (13) und Spreizfaktor siehe Gl. (73) - ₁ 1. Nullstelle der FunktionJ ₀, ₁=2,405 - Faktor für die dynamische Rückstromdichte Gl. (39) - Wandkorrekturfaktor für die Ladungsträgerdichte Gl. (1) - _i Raumladungsdichte in der Sperrschicht - definiert in Gl. (73) Die Ergebnisse der vorliegenden Arbeit werden in der im Arch. f. Elektrotechnik 49 (1964), H. 4, erscheinenden Theorie der Rückzündung bei Quecksilberdampf-Stromrichtergefäßen angewendet.     

Electrical properties of PZT piezoelectric ceramic at high temperatures

Advanced aeronautic and space structures need active components that can function at high frequencies and temperatures. Piezoelectric materials can provide frequency response but their use at elevated temperatures is limited. The reason for the lack of insertion of piezoelectric for high temperature active component and sensors are two fold. First, the database of piezoelectric properties that describe the piezoelectric constants is lacking for high temperatures engineering applications. Most studies measure the dielectric constants to determine the Curie temperature but do not provide piezoelectric coefficients as a function of temperature. Second, piezoelectric materials with Curie temperature (T _C) exceeding 500 °C are sought for aeronautics and aerospace applications. This investigation describes a measurement system that captures the impedance dependence upon temperature for piezoelectric materials. Commercially available lead zirconate titanate (PZT) was studied as to determine the piezoelectric activity to define the operating envelope with respect to temperature. The elastic properties , piezoelectric coefficients , dielectric properties , and electro-mechanical coupling factors were determined as a function of temperature. The coupling factor k ₃₃ was found to be relatively constant to 200 °C and exhibit slight temperature dependence above 200 °C. The temperature sensitivity for both piezoelectric coefficient and electromechanical coupling factor were very small; the slopes and Δk ₃₃/k ₃₃ were found to be 0.01 and (−0.07) respectively in the range of 120 to 200 °C. This measurement technique will populate databases that describe the piezoelectric properties of commercially available PZT piezoelectric materials. It can also facilitate the assessment of new piezoelectric materials that are currently being developed for higher temperature applications. This work is supported by US Air Force grant F49620-03-1-0128.     

Computational analysis of the contributions to the piezoelectric coefficient e_{33} in ZnO nanowires: first-principles calculations

We investigated the piezoelectric coefficient, \(e_{33} \) , of ZnO nanowires, subdividing it into an ionic term, \(e_{33}^{\text {ion}} \) , and an electronic term, \(e_{33}^{\text {el}} \) , and calculated the effects of different diameters on its value using ab initio density functional theory calculations. The \(e_{33}^{\text {ion}} \) term was found to be dominant, with the innermost (outermost) atoms in the nanowires making the largest (smallest) contribution to the term. Moreover, the density of states (DOS) and projected DOS data revealed that the DOS tends to increase at the valence band maximum in the case of the outermost atoms, where the O \(2p\) and Zn \(3d\) orbital peaks increase in magnitude, resulting in hybridization and a decrease in bond length.     

Boundary condition at the junction

When modeling a 2-d quantum network by a 1-d quantum graph one usually substitutes the 2-d vertex domains by the point-wise junctions with appropriate boundary conditions imposed on the boundary values $ \vec{\psi}(a) = (\psi_1 (a),\, \psi_2 (a),\, \psi_3 (a), \ldots \psi_n (a) ),\,\, \vec{\psi}' = (\psi'_1 (a),\, \psi'_2 (a),\, \psi'_3 (a), \ldots \psi'_n (a) ) $ of the wave-function on the leads $ \omega_1,\, \omega_2,\ldots \omega_n$ at the junction a. In particular Datta proposed parametrization of the boundary condition, for symmetric T-junction, by some orthogonal 1-d projection $ P_0: R_n \to R_n $ $$ P_0^{\bot}\,\,\vec{\psi}(a) = 0,\quad P_0\,\,\vec{\psi}'(a) = 0. $$ We consider an arbitrary junction, $ n \geq 3$ , of 2-d leads attached to a 2-d vertex domain $\Omega_{int}$ , in case, when there exist a resonance eigenvalue $\lambda_0 = 2 m^* E_f \,\hbar^{-2}$ of the Schrödinger operator $L_{int}$ . We derive, from the first principles, energy-dependent boundary conditions for thin, quasi-1-d, network, and obtain from it, in the limit of zero temperature, Datta-type boundary condition, interpreting the projection P ₀ in terms of the resonance eigenfunction $\psi_0: L_{int} \psi_0 = \lambda_0 \psi_0$ and geometry of the leads.     

Epitaxial growth of multilayered (Bi,La)4Ti3O12/Pb(Zr,Ti)O3 ferroelectric thin films with different orientations

Epitaxial (Bi,La)₄Ti₃O₁₂ (BLT) thin films, epitaxial Pb(Zr,Ti)O₃ (PZT) thin films, and epitaxial multilayered BLT/PZT ferroelectric thin films with different orientations were prepared on SrTiO₃ (STO) single crystal substrates by pulsed laser deposition. From X-ray pole-figures and electron diffraction patterns, the epitaxial orientation relationships between BLT layers, PZT layers, and STO substrates were identified to be (1) BLT(001)//PZT(001)//STO(001), and BLT[110]//PZT[100]//STO[100] for the multilayered thin films on (001)-oriented STO substrates, and (2) BLT(118)//PZT(011)//STO(011), and $ {\text{BLT}}{\left[ {\overline{1} \overline{1} 0} \right]}//{\text{PZT}}{\left[ {100} \right]}//{\text{SrTiO}}_{3} {\left[ {100} \right]} $ for the multilayered films on (011)-oriented STO substrates. Tri-layered films of the same compositions showed well-defined hysteresis loops as well as a high fatigue resistance up to 1?×?10¹⁰ switching cycles.     

Photoluminescence and Raman spectroscopy characterization of highly c-axis oriented MgxZn1?xO thin films on Pt-coated silicon substrates

Highly c-axis oriented $ {\text{M}}{{\text{g}}_{\text{x}}}{\text{Z}}{{\text{n}}_{{1 - {\text{x}}}}}{\text{O}}\left( {x = 0 \sim 0.2} \right) $ thin films with pure hexagonal phase were prepared on Pt/TiO₂/SiO₂/Si substrates by chemical solution deposition method, and their structure, photoluminescence, and lattice vibrational properties were studied. For the thin films with Mg contents ranging 0????x????0.20, the room-temperature near-band-edge emission exhibited blueshift up to about 0.35 eV, indicating that the band-gaps of thin films could be tailored by Mg incorporation, meanwhile, the green emission of the thin films enhanced with increasing Mg content. Raman spectra analysis indicated that the decreasing high frequency E₂ Raman modes showed composition-dependent asymmetrically broadening. The difference of electronegativity between Mg²⁺ for Zn²⁺ as well as the potential fluctuation were discussed. Furthermore, longtitudial optical modes exhibited one-mode behavior with observed ~25.8 cm^?1 blueshift. X-ray photoelectron spectroscopy measurements clearly confirmed the Mg incorporation.     

Structure and microwave dielectric properties of Sm(2−x)/3Li x TiO3

The structural evolution, and microwave dielectric properties of ceramics (x = 0.0 ≤ x ≤ 0.5) were investigated in this work. X-ray diffraction (XRD) results show that samples with x > 0.3 exhibit a single perovskite phase. Impurity phases of Sm₂Ti₂O₇ and TiO₂ appear and their amount increases with the decrease of x when x ≤ 0.3. TEM observation indicates that the A-site is ordered in x = 0.5, but not in x = 0.3). The dielectric constant decreases with the increase of x for 0.1 ≤ x ≤ 0.4 and then increases with further increase in x up to x = 0.5. The Q×f value decreases with the decrease of x due to the increased occurrence of Sm₂T₂O₇ secondary phase, defects and twinning boundaries. The temperature coefficient of resonant frequency is negative and its absolute value decreases greatly with the decrease of x value.     

Synthesis and properties of SDC powders and ceramics for low temperature SOFC by stearic acid process

Ce_0.8Sm_0.2O_1.9 (SDC) powders were prepared by a novel solution combustion process using molten stearic acid as dispersive medium and reducing agent. The powders prepared with the molar ratio of $ {\text{NO}}^{ - }_{{\text{3}}} $ to stearic acid at 1:1.5 exhibited a narrower distribution in sizes and the average agglomerate size is about 157 nm. The non-agglomerated particles are in the range 10–40 nm. The as-combusted powders prepared by the present method were pure oxides powder with low crystallinity, which exhibited excellent sintering properties, easily achieving high dense SDC ceramics with lager grains (0.85 μm).     

Analytical evaluation of the charge carrier density of organic materials with a Gaussian density of states revisited

An analytical solution for the calculation of the charge carrier density of organic materials with a Gaussian distribution for the density of states is presented and builds upon the ideas presented by Mehmeto?lu (J Comput Electron 13:960–964, 2014) and Paasch et al. (J Appl Phys 107:104501-1–104501-4, 2010). The integral of interest is called the Gauss–Fermi integral and can be viewed as a particular type of integral in a family of the more general Fermi–Dirac-type integrals. The form of the Gauss–Fermi integral will be defined as

$$\begin{aligned} G\left( \alpha ,\beta ,\xi \right) =\mathop {\displaystyle \int }\limits _{-\infty }^{\infty }\frac{ e^{-\alpha \left( x-\beta \right) ^{2}}}{1+e^{x-\xi }}\hbox {d}x\text {,} \end{aligned}$$

where \(G\left( \alpha ,\beta ,\xi \right) \) is a dimensionless function. This article illustrates a technique developed by Selvaggi et al. [3] to derive a mathematical formula for a complete range of parameters \(\alpha \), \(\beta \), and \(\xi \) valid \(\forall \) \(\alpha \) \( \varepsilon \) \( {\mathbb {R}} \ge 0\), \(\forall \) \(\beta \) \(\varepsilon \) \( {\mathbb {R}} \), and \(\forall \) \(\xi \) \(\varepsilon \) \( {\mathbb {R}} \).

     

Electrical properties of rutile-type relaxor ferroelectric-like Fe0.9W0.05TiMO6 (M = Ta,Nb) ceramics

Electrical properties of rutile-type $\mathrm {Fe}_{0.9}{\kern 1pt} \mathrm {W}_{0.05}\\\mathrm {TiMO}_{6} (\mathrm {M} {} = {} \mathrm {Ta,Nb})$ ceramics were measured at and above room temperature and the results are compared with those gained previously on rutile-type relaxor ferroelectrics $\mathrm {FeTiMO}_{6} (\mathrm {M} {} = {} \mathrm {Ta,Nb})$ . The aliovalent ${\rm W}^{6+}$ cationsin the current compounds might change the suggested polar nanodomains, giving rise to very high dielectric constant $\epsilon (\omega )$ , and further electrical quantities can possibly shed additional light on the nature of the mechanism leading to extraordinary values in $\epsilon (\omega )$ . In part similar electrical data were established such as very high $\epsilon (\omega )$ but also different results were noted. Apart from $\epsilon (\omega )$ , the electrical response was analysed by measuring losses, dissipation factor $\tan \delta $ , DC conductivity $\sigma _{DC}$ and AC conductivity $\sigma _{AC}(\omega )$ using impedance spectroscopy, and thermopower; the results are discussed in conjunction with literature data. The role of grain boundaries and sample-electrode processes was investigated in particular with respect to the sample capacitance. Eventual microstructural local inhomogeneities were checked by means of ⁵⁷Fe Mössbauer spectroscopy. For both compounds, the temperature dependence of bulk $\sigma _{DC}$ showed Arrhenius behaviour with activation energy ${E_{A}}\sim $ 0.35 eV and $\sigma _{DC}$ (295 K) $\sim 5\times 10^{-5} \Omega ^{-1}\text{cm}^{-1}$ ; grain boundaries exhibited slightly higher ${E_{A}}$ but the value of $\sigma _{DC}$ was a factor of up to $\sim 10$ lower at all temperatures. From $\sigma _{AC}(\omega )$ data, a power law frequency dependence of grain boundary conductivity was derived. Relaxation processes were established from loss and $\tan \delta $ data. The thermopower is negative and varies weakly with temperature, pointing to long-range charge transfer by a hopping-type mechanism of electron polarons.     

Structural stability of multiferroics BiMnO3 under high pressure

Multiferroics BiMnO₃ was fabricated via high pressure of 4 GPa. The crystal structure of as-prepared specimen was determined by x-ray diffraction to be highly distorted monoclinic perovskite with space group of C2. Multiferroism (or ferroelectromagnetism, i.e., coexistence of ferromagnetism and ferroelectricity) in as-prepared specimen has been reported in the recently published paper (Z.H. Chi, C.J. Xiao, S.M. Feng, F.Y. Li, C.Q. Jin, J. Appl. Phys. 98:103519, 2005). Structural toughness of as-prepared specimen under high pressure was studied in diamond-anvil cell (DAC) combined with synchrotron radiation x-ray diffraction. No structural phase transition was detected up to the maximum pressure of 27 GPa, indicating a compact and low compressibility of monoclinically distorted perovskite structure of BiMnO₃. The bulk modulus B ₀?=?141 GPa ( $ B^{\prime }_{{\text{0}}} = {\text{4}} $ ) was derived from Birch–Murnaghan equation of state (EOS).