Oscillating magnetoresistance of (Bi,Pb)2Sr2Ca2Cu3O x ceramics doped with Mn

The magnetoresistance nearT _c(T _cR=0=100 K) has been measured on ceramic samples of (Bi, Pb)₂Sr₂Ca₂(Cu_0.98Mn_0.02)₃O_x (X-Ray diffractions and measurements by a SQUID magnetometer give almost single 2223 phase) in magnetic fields, up to 60 kOe using a dc four-probe technique. We observed periodic oscillations superimposed on a monotonie growth of the magnetoresistance with the amplitude decreasing with increase in magnetic field. Fourier transforms of the magnetoresistance data gives two sharply pronounced periods, 10.7 and 14.7 kOe. Apparently these oscillations are connected with inhomogeneous distributions of Mn in superconducting grains with phase slippage at grain boundaries.     

Ba,Sr掺杂对K0.47Na0.47Li0.06NbO3基无铅压电陶瓷结构、介电及压电性能的影响

采用传统的固态反应法制备了(K0.47Na0.47 Li0.06 )1-x(Ba0.5Sr0.5)xNbO3无铅压电陶瓷,研究了Ba,Sr掺杂对K0.47Na0.47Li0.06NbO3陶瓷的晶体结构、电畴结构、介电及压电性能的影响.随着Ba,Sr掺杂量的增加,陶瓷样品逐渐由正交相向四方相转变,同时居里温度(Tc)降低,剩余极化率(Pr)、矫顽场(Ec)、介电常数(εr)增加;压电常数(d33)、机电耦合系数(kp)先增加后减小.x=0.5％时陶瓷的压电常数d33达到221 pC/N,机电耦合系数kp为43.1％.     

Microstructure and properties of (Sr,Ca)CuO2/(Sr,Ca)RuO3 multilayers

Epitaxial multilayer thin films of “infinite-layer” (Sr, Ca)CuO₂ and perovskite (Sr, Ca)RuO₃ have been prepared on (100) SrTiO₃ substrates by multitarget rf magnetron sputtering. X-ray diffraction analyses revealed that the multilayer structure of (Sr, Ca)CuO₃/(Sr, Ca)RuO₃ was successfully fabricated with a minimum layer thickness of 20 Å. Transmission electron microscopy measurements of the multilayers indicated that there was no dislocation which normally exists in single-layer films with an infinite-layer structure. Resistivities of multilayer films at room temperature ranged from 1 to 10 mΩ cm and showed semiconductor-like dependence against the temperature.     

Processing and characterization of A-site deficient [(Ca,Sr) x (La,Nd)2/3−2x/3]TiO3 dielectric ceramics

A-site deficient perovskite ceramics in the [(Ca, Sr) _x (La, Nd)_2/3?2x/3]TiO₃ (x = 0.1–0.9) system were prepared by a mixed-oxide solid state sintering route. Synchrotron X-ray diffraction and Raman spectroscopy revealed a tetragonal (I4/mcm) symmetry for the compositions with x = 0.1–0.7 and orthorhombic (Pbnm) symmetry for the x = 0.8 and 0.9 compositions. The grain size increased with an increase in x up to 0.7 and then decreased upon further increase in x to 0.8 and 0.9. The optimum microwave dielectric properties (ε_r ~ 48, Q × f = 3,664 GHz and τ _f  ~ +61 GHz) were recorded for the compositions with x = 0.1.     

Electrical properties of (Ba,Sr)TiO3 on (Sr,Ca)RuO3 electrode

A perovskite (Sr,Ca)RuO₃ [SCR] electrode has been explored in order to utilize its advantages in structural match with (Ba,Sr)TiO₃ [BST] films, which may enhance the electrical properties of BST films. The SCR electrode led to the leakage current density (10^–7 A/cm²) of BST films an order lower than that on RuO₂. The leakage current was not sensitive to the composition of the SCR electrodes, while the dielectric constant of the BST thin film capacitor ranged from 160 to 280 depending on the Sr/Ca ratio in SCR electrodes. The BST/SCR (Sr/Ca = 7/3) system resulted in a 5–nm thick interfacial layer. Furthermore, the interfacial layer turned out to be partially crystallized according to the lattice image taken by an HRTEM. It is believed that such enhancement in electrical properties of BST films could be induced by the improvement of interfacial characteristics through structural matching.     

Synthesis and Structure of (Ca,Sr)-Substituted Lanthanum Manganite

The phase composition and structure of equilibrium LaMnO₃-CaMnO₃-SrMnO₃ samples prepared at 1500°C in air are investigated. The results demonstrate that the system contains a broad region of La_{1 − x} (Ca_{1 − y} Sr_y)_xMnO₃ perovskite-like solid solutions in which calcium and strontium cations substitute for lanthanum. The solid solutions have an orthorhombic (Pnma), rhombohedral , or tetragonal (I4/mcm) structure, depending on the A-site cation composition and the nature of lattice distortions. The composition regions of these structures and two-phase regions are mapped out in the LaMnO₃-CaMnO₃-SrMnO₃ phase diagram.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 8, 2005, pp. 990–997.Original Russian Text Copyright © 2005 by Slobodin, Vladimirova, Petukhov, Surat, Leonidov.     

Characterization and properties of antimony doped Bi1.6Pb0.3Sr2Ca3Cu4O x ceramics

The influence of Sb₂O₃ dopant on the superconductivity and the phase formation of the Bi(Pb)-Sr-Ca-Cu-O system was studied using differential thermal analysis/thermogravimetric analysis (DTA/TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM), a.c. susceptibility and resistance measurements. It was found that the solubility of Sb³⁺ in the 110 K superconducting phase is limited; instead Sb³⁺ readily combines with other elements to form one or more unknown second phase(s), which melt at lower temperatures and accelerates the formation of the 110 K phase. Resistance measurements show the transition initiation temperature of the 110 K superconducting phase is unchanged but thatT _c (zero) was found to decrease from 107 K to 98 K. TEM examination generating lattice images from antimony-doped crystals, showed the structure to be inhomogeneous and to contain many defects.     

Scintillating properties of pure and doped BGO ceramics

The ceramic processing and characterization of Bi₄Ge₃O₁₂ pure and doped with Eu³⁺ and Nd³⁺ was performed in order to investigate its potential use in radiation detector devices. Single phase Bi₄Ge₃O₁₂ in pure state and containing 1% of the dopands Nd³⁺ and Eu³⁺ were produced via a solid state route and their photoluminescent and radioluminescent properties were investigated. When excited at 200–230 nm, pure BGO ceramics presented a wide photoluminescent band emission centered at 450 nm, assigned to the Bi³⁺ internal transitions. For the doped samples under the same excitation, this wide band was superposed by the emission peaks of the rare earth dopands, at around 600 nm for BGO:Eu³⁺ and at 350 nm, 430 and 600 nm for BGO:Nd³⁺. Radioluminescence measurements presented similar results and allowed the determination of the light output efficiency of the three scintillators. The values determined were 4 × 10³ photons/MeV for BGO:Nd and 5.9 × 10³ photons/MeV for BGO:Eu, which are higher than the value 3.9 × 10³ photons/MeV determined previously for the pure ceramic. A selective sensibility of the BGO:Eu ceramics to the nature and energy of the radiation, which is not observed in pure samples, was also presented and discussed.     

Synthesis and characterization of Zn-B-Si-O nano-composites and their doped BaTiO3 ceramics

We synthesized Zn-B-Si-O (ZBSO) nano-composites via sol-gel process, and then used them to dope BaTiO₃ ceramics. The ZBSO nano-composites and their ceramics were characterized by means of thermogravimetric, Fourier-transform infrared, and X-ray diffraction methods, and using scanning and transmission electron microscopy. We also characterized the dielectric properties of the ceramics. The results indicated that the ZBSO nano-composites were nanometer-scale powders with an amorphous structure. The particle size of the powders increased with increasing pH value, but initially decreased and then increased with increasing calcining temperature. At pH about 2 and with calcining at 400 °C, the nano-composites attained minimum particle size (about 30 nm). The sintering temperature of the BaTiO₃ ceramics could be reduced to 1100 °C by adding 5 wt% of the ZBSO nano-composites. Uniform, fine-grained BaTiO₃ ceramics with a high permittivity (?_r = 2946 and ?_max = 5072) were obtained by adding nano-composites; these properties were superior to the ZBSO glass doped BaTiO₃ ceramics.     

Synthesis, IR, crystallization and dielectric study of (Pb, Sr)TiO 3 borosilicate glass–ceramics

Eleven glass compositions were prepared by melt and quench method with progressive substitution of SrO for PbO (0?≤?x?≤ 1·0) with a step-wise increment of 0·10 in the glass [(Pb _x Sr_1???x )OTiO₂]–[(2SiO₂B₂O₃)]–[BaO·K₂O]·Nb₂O₅ (mol percentage) system. The infrared spectra (IR) of various glass compositions in the above mentioned glass system was recorded over a continuous spectral range 400–4000 cm^???1 to study their different oxides structure systematically. Differential thermal analysis (DTA) was recorded from room temperature (~27 °C) to 1400 °C employing a heating rate of 10 °C /min to determine glass transition temperature, T _g and crystallization temperature, T _c. The melting temperature, T _m, of these glass compositions was found to be in the range 597–1060 °C depending on the composition under normal atmospheric conditions. T _g and T _m of glasses were found to increase with increasing SrO content. X-ray diffraction analysis of these glass–ceramic samples shows that major crystalline phase of the glass–ceramic sample with x ≤ 0·5 was found to have cubic structure similar to SrTiO₃ ceramic. Scanning electron microscopy has been carried out to see the surface morphology of the crystallites dispersed in the glassy matrix.     

La3+掺杂对(Sr,Ba,Ca)TiO3基压敏陶瓷结构和性能的影响

采用常规固相法制备(Sr,Ba,Ca)TiO3基压敏陶瓷.用Nb5 离子取代Ti4 离子,Mn作受主掺杂元素的前提下,系统研究了稀土离子La3 施主掺杂对压敏陶瓷结构和性能的影响.结果表明,当La2O3=0.4%(摩尔分数)时,(Sr,Ba,Ca)TiO3基压敏陶瓷可获得良好的电性能:其压敏电压V10mA=11.19V,非线性系数α=2.93,电容C=31.16nF,介电损耗tanδ=0.43%,压敏电压温度系数KV10mA=0.1%/℃.     

Synthesis and properties of magnetoresistive (La,Sr)MnO<Subscript>3</Subscript>-based glass-ceramic borate-matrix composites

Magnetic glass-ceramic borate-matrix composites containing micron-sized lanthanum strontium manganite grains have been prepared by ceramming amorphous La₂O₃-SrO-MnO _x -B₂O₃ materials at 800 and 900°C. The glass-ceramics had a magnetization of up to 48.7 A m²/kg in a magnetic field of 400 kA/m. Their relative magnetoresistance reached 6.2% at 290 K in a magnetic field of 80 kA/m and 16% at 77 K in a field of 160 kA/m.     

Polarization-induced photoluminescence variation in Pr3+- doped (Ba,Ca)(Ti,Sn)O3 ferroelectric ceramics

The development of multifunctional optical materials can meet the huge demands of modern optics. Generally, it is difficult to achieve multiple optical properties in one material. In this work, we choose ferroelectric (Ba, Ca)(Ti, Sn)O₃ ceramics as the hosts, which are doped with rare earth ion Pr³⁺. The integration of photoluminescence, ferroelectricity, and piezoelectricity is realized in the Pr³⁺-doped (Ba, Ca)(Ti, Sn)O₃ ferroelectric ceramics. The Pr-BCTS ceramics show excellent piezoelectric properties (Pr-BCTS-I: d₃₃?=?210 pC/N; Pr-BCTS-II: d₃₃?=?350 pC/N). Under 449 nm light excitation, all samples show strong orange-red emission centered at 603 nm, 617 nm, and 643 nm. Photoluminescence performance of the Pr-BCTS-I ceramics with orthogonal and tetragonal phase structure increases after polarization treatment, while that of the Pr-BCTS-II ceramics with rhombohedral and tetragonal phase structure after polarization treatment declines. The mechanism of luminescence modulation and polarization processing is discussed. Current research can provide a feasible example to achieve photoluminescence tunability in a material.

     

Synthesis,characterization, thermal and dielectric properties of pure and cadmium doped calcium hydrogen phosphate

The synthesis of pure and cadmium doped calcium hydrogen phosphate as single crystal has been accomplished by a room temperature solution growth technique viz., silica gel technique. Silica gel obtained from sodium metasilicate with a strongly acidic cation exchanger in the H-form, was used for crystal growth experiments. The nature of the grown material was established by powder X-ray diffraction (PXRD) studies, whereas from single crystal X-ray diffraction (SXRD) the crystal system comes out to be monoclinic. The stoichiometry of the grown composition was established by energy dispersive X-ray analysis (EDAX). Fourier transform infrared spectroscopic (FTIR) studies signifies the presence of phosphate (PO₄)²⁻ group and water of crystallization. Thermo gravimetrical analysis and investigations of dielectric properties were undertaken to study the thermal stability, dielectric constant and transition temperature of the grown material. Dielectric studies suggest that there is a shift in the value of transition temperature (T_c) thereby indicating relaxor behaviour of the material.     

(Sr,Ca)TiO3陶瓷材料的结构与介电性能

研究(Sr,Ca)TiO₃系统陶瓷材料的组成、结构与介电性能关系.当ST/CT比值约为7:3时,主晶相(Sr_0.7Ca_0.3)TiO₃形成完全互溶钙钛矿型固溶体,具有立方顺电相结构;系统中微量钨青铜型新化合物铌酸钛钡BTN对主晶相(Sr_0.7Ca_0.3)TiO₃的介电性能起进一步的改善作用.获得具有理想介电性能(ε_(20℃1MHZ)>250,α_{c(-55～+125℃)}=-1150ppm/℃,tgδ_(20℃1MHZ)<5×10^-4,ρ_{v(20℃100VDC)}>10¹³Ω·cm)、不含Pb、Bi的Q组MLC瓷料.