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对电脉冲诱导的不同电阻态下La0.7Ca0.3MnO3样品的比热进行了研究.实验结果表明,电脉冲导致La0.7Ca0.3MnO3样品比热随电阻状态发生可逆变化.比热随电阻状态的减小而减小.低温比热拟合及不同电阻状态下的比热差与温度关系说明,声子对比热的贡献不随电阻状态变化,磁性和载流子对比热的贡献是导致La0.7Ca0.3MnO3样品比热变化的原因.电脉冲诱导O离子沿一维扩展性缺陷的电化学迁移,导致材料中局部区域的O离子浓度发生变化.O离子浓度的变化导致载流子浓度的变化,同时载流子浓度的变化将使得低温下磁性耦合强度发生变化,从而导致比热发生变化. 相似文献
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采用固相反应法制备了不同含氧量的BiFeOδ多晶陶瓷样品,利用HP4294A阻抗分析仪测量了样品的介电特性随频率和氧含量的变化,用正电子湮没寿命谱学的方法研究了样品中因氧含量的变化所引起的结构缺陷. 实验结果表明:引入氧空位和氧填隙离子缺陷都会使介电常数减小,而介电损耗则随氧含量的增加而增加,二者的变化范围均在10%—35%之间;对不同氧含量的BiFeOδ样品,介电常数和介电损耗随测量频率的增加而减小. 氧空位的引入使得局域电子密度变小,正电子平均寿命τm增加. 在氧含量δ=2.99时电子密度最大(ne=3.90×1023/cm3),继续增加氧含量对正电子寿命与局域电子密度的影响不大. BiFeOδ样品的介电常数和介电损耗随氧含量的变化可以在空间电荷限制电导的框架下来理解. 相似文献
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采用组合材料方法制备并筛选了具有高红外辐射性能的Ba/Fe共掺堇青石固溶体(Ba0.05Fe0.1Mg)2Al4Si5O18. 通过组合溶液喷射法,制备了7×7阵列的样品库,并在不同温度下进行热处理.通过X射线衍射、红外热成像等测试方法分析了Ba2+、Fe3+固溶对堇青石晶格畸变和红外辐射性能的影响. 经过放大制备实验的验证,确定了材料的最佳组分为5%Ba2+和10%Fe3+共固溶的堇青石. 最佳组分样品在100 oC时的红外辐射率在5-24 μm波段均高于0.8. 相似文献
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利用传统固相反应方法, 分别在1440℃, 1460℃, 1480℃和1500℃烧结条件下, 制备了钙钛矿结构的La0.1Sr0.9TiO3陶瓷样品. 样品的粉末X射线衍射结果显示, 不同烧结温度的La0.1Sr0.9TiO3 陶瓷样品均为单相的正交结构. 从样品的扫描电子显微照片来看, 随着烧结温度的增加, 平均晶粒尺寸逐渐增大. 在室温至800℃的测试温区, 测试了样品的电阻率和Seebeck系数, 系统地研究了不同烧结温度对样品热电性能的影响. 结果表明, 样品的电阻率在测试温区内随着测试温度的升高先略微降低, 然后逐渐升高;总体来看, 样品的电阻率随烧结温度的升高先增大后降低. 在测试温区内, Seebeck系数均为负值, 表明样品的载流子为电子; 随着测试温度的升高, Seebeck系数绝对值均有所增大;随烧结温度升高, Seebeck系数绝对值逐渐增大后显著降低. 1480℃制备的样品因其相对较低的电阻率和相对较高的Seebeck系数绝对值, 在165℃时得到最大的功率因子21 μW·K-2·cm-1. 相似文献
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采用脉冲激光沉积方法在(LaAlO3)0:3(Sr2AlTaO6)0:7衬底上外延生长了La0.7Sr0.3MnO3薄膜,并采用慢正电子束方法分析了薄膜在不同厚度和不同退火气氛下参数S的变化. 分析表明,薄膜中包含两种机制引入的氧空位,分别是薄膜生长气氛中氧压偏低造成薄膜的氧缺乏和由于薄膜应变引入空位型缺陷. 当薄膜厚度较薄时,应变造成的晶格畸变化比较大,当薄膜的厚度大于11 nm时,薄膜的应变驰豫已经比较完全. 原位退火的样品中正电子主要是被氧缺乏引起的氧空位捕获. 在氧气中退火的样品,S随厚度的变化反映了应变对薄膜微结构的影响. 相似文献
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Thin films of Ba1−xLaxTiO3 on platinum substrates were synthesized using the sol–gel method for x values of 0.0, 0.03, 0.05, and 0.10, and the effect of trivalent La3+ substitution on the structural and dielectric properties was studied. Using X‐ray diffraction, structural analysis of these compositions revealed a slight increase in the tetragonal distortion of the unit cell with increase in La content. Accordingly, an increase in the tetragonal to cubic transition temperature TT/C was detected by temperature‐dependent Raman spectroscopy in the range of 70–500 K. Unlike the results from Raman scattering for the La‐doped BaTiO3 films, the dielectric measurements showed broad and diffused dielectric maxima, making the estimation of the transition temperature merely qualitative. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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The small-signal ac response of single crystalline Ba1?xLaxF2+x solid solutions has been studied in the temperature region 300–820 K, and in the frequency range 4×10?2–5×104 Hz. At low temperatures the frequency dispersion is dominated by processes in the bulk. Apart from the bulk conductance these processes include a dielectric response determined by broad distributions of dipole-like relaxations. The increase of the static dielectric constant with increasing solute content is explained. At higher temperatures the frequency dispersion reflects interfacial phenomena. In addition to an almost ideal interface capacitance, phenomena are observed which indicate the growth of a surface layer due to a reaction between the electrolyte, and residual oxygen and/or water vapour from the ambient. 相似文献
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Dielectric constant, dielectric loss and AC conductivity were measured, in the frequency range 100 Hz to 5 MHz in chlorinated poly (vinyl chloride) (CPVC) before and after exposure to gamma irradiation at doses between 5.0 KGy and 50.0 KGy. The frequency dependencies of ε′, ε″ and σAC at 30 °C were investigated. A relaxation peak in the dielectric loss and a corresponding step in the dielectric constant have been observed, in the frequency ranges 103 Hz to 104 Hz. The dielectric constant ε′, dielectric loss ε″ and AC conductivity σAC are also found to increase at heating up to 100 °C. In addition the effect of gamma irradiation on the frequency dependencies of ε′, ε″ and σAC was measured at room temperature. The gamma irradiation leads to an increase in the efficiency of soft segments. Furthermore, the DC electrical conductivity of both the irradiated and non-irradiated samples was investigated. The induced electrical conductivity and the activation energy were measured, at various temperatures, as a function of gamma dose. It was found that the gamma radiation has a definite effect on the DC conductivity of the CPVC polymer. 相似文献
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In this study, effect of lanthanum substitution on the phase composition, lattice parameters and magnetic properties of barium hexaferrite has been studied in samples synthesized in ammonium nitrate melt. Samples, prepared with different lanthanum amount and having various initial Fe/(Ba+La) ratios in between 12 and 2 {(Ba1−xLax)·n Fe2O3, where 0≤x≤1 and 1≤n≤6)}, are sintered at temperatures from 800 to 1200 °C. The lattice parameters, both a and c, decreases with increasing La amount which results in a decrease of the unit cell volume. The scanning electron microscope micrographs show that the pure and La-substituted sample with x=0.3, both calcinated at 1000 °C, have grain sizes smaller than 1 μm. The coercivities of the La-substituted samples increase with increasing La amount and reaches to a maximum value of 5.73 kOe, when x=0.3. Sintering at higher temperatures (above 1000 °C) decreases the coercivity, resembling a transition from single to multi-domain behavior of the particles, while saturation magnetization of the samples continues to increase due to the increasing grain size. Magnetization measurements of the samples prepared with different Fe/(Ba+La) molar ratios, n's, revealed that the specific saturation magnetization slightly increases with decreasing n, while coercivities fluctuates around 5.5 kOe. However, a sharp increase in the saturation magnetization has been observed in the sample having n=1 and washed in HCl. It was measured as 59.2 emu/g at 15 kOe, which is higher than that of the pure sample (57.5 emu/g). Thus, the magnetic parameters are optimized in the sample Ba0.7La0.3Fe12O19 so as to maximize both coercivity and specific saturation magnetization in the HCl-washed sample synthesized by starting with an unusually low Fe/(Ba+La) molar ratio of 2 (or n=1). 相似文献
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M.M. Savosta A.N. Ulyanov N.Yu. Starostyuk M. Maryško P. Novák 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(3):393-396
The results of 55Mn NMR, dc magnetization, and ac susceptibility studies are presented for La0.7Ca0.15Ba0.15MnO3, La0.7Sr0.15Ba0.15MnO3, and La0.7Ba0.3MnO3 ferromagnetic manganites. While is a function of the mean radius of the La and alkaline-earth ions and the cation disorder, the form of the temperature dependence
of the magnetic moment may be expressed as function of only. The phase transition is continuous for all three compounds.
Received 5 March 1999 相似文献
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Abstract A crystal chemical study has allowed us to identify new niobochromates crystallizing with the tungsten bronze structure: Ba2LnNb4CrO15 (Ln = Bi, La), La2ANb4CrO15 (A = Li, Na, K) and Ba2Na1-x La x Nb5-x Cr x O15 (0 ? x ? 1). A dielectric study has shown that the T c (x) curve goes through a minimum at x ? 0.5 along the solid solution Ba2Na1-x La x Nb5-x Cr x O15, while the ferroelastic transition Tc changes very slightly in the same range of composition. 相似文献
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The dielectric, optical and non-linear optical properties of Ba6Ti2Nb8O30 single crystals were examined from room temperature up to the Curie temperature of 245°C. The spontaneous polarization at room temperature was estimated as 0·22±0·01 C/m2. The linear electrooptic constants were measured as r33T=(1·17±0·02)×10?10 and r13T=(0·42±0·01)×10?10 m/V. The non-linear optical coefficients were d33=(15·1±2·0)×10?12 and d31=(11·0±2·0)×10?12 m/V, which are comparable to those of Ba4Na2Nb10O30. Temperature dependences of δ33 and δ31 (Miller's δ) were found to be proportional to that of Ps. 相似文献
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Way Foong Lim Zainovia Lockman Kuan Yew Cheong 《Applied Physics A: Materials Science & Processing》2012,107(2):459-467
Metal-organic decomposed lanthanum cerium oxide (La
x
Ce
y
O
z
) film had been spin-coated on n-type Si substrate. Effects of post-deposition annealing temperature and time on the metal-oxide-semiconductor
(MOS) properties of the film were studied. As temperature increased from 400 to 1000°C for 15 minutes dwell time, La
x
Ce
y
O
z
demonstrated a decrease in interface trap density (D
it) and total interface trap density (D
total), which were related to the formation of SiO
x
/silicates interfacial layer (IL). The lowest leakage current density and highest dielectric breakdown voltage (V
B) was obtained in 1000°C-annealed sample. When longer annealing times (30–120 minutes) were studied on the 1000°C-annealed
sample, the sample annealed at 1000°C for 120 min showed the best MOS characteristics with V
B of 30 V. Reasons contributing to such observation were discussed. 相似文献
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(001)La0.67Sr0.33MnO3/(001)(BaxSr1 ? x TiO3/(001)La0.67Sr0.33MnO3(x= 0–0.25) three-layer heterostructures are grown by laser evaporation on (001)La0.3Sr0.7Al0.65Ta0.35O3 single-crystalline substrates. In a wide temperature range (≈150 K), effective permittivity ? of (1000 nm)Ba0.25Sr0.75TiO3 and (1000 nm)SrTiO3 films grown obeys the relationship ? ~ (T ? T CW)?1, where T CW is the Curie-Weiss temperature for related bulk crystals. Using experimental dependences ?(T), the capacitance of the (001)La0.67Sr0.33MnO3/(001)BaxSr1?x TiO3 and (001)La0.67Sr0.33MnO3/(001)SrTiO3 interfaces, which is due to electric field penetration into the manganite electrode, is estimated (C int≈4μF/cm2). At bias voltages of ± 2.5 V, the change in the permittivity of the STO and BSTO films in the heterostructures studied reaches 25 and 45%, respectively. 相似文献
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The structure and dielectric parameters of the intermediate ferroelectric layer in the (001)SrRuO3 ∥ (100)Ba0.75Sr0.25TiO3 ∥ (001)SrRO3 heterostructure grown by laser ablation on (001)La0.294Sr0.706Al0.647Ta0.353O3 were studied. Tensile mechanical stresses accounted for the polar axis in the ferroelectric, being oriented predominantly parallel to the substrate plane. The remanent polarization in the Ba0.75Sr0.25TiO3 layer increased approximately linearly with decreasing temperature in the interval 320–200 K. The real part of the dielectric permittivity of the intermediate ferroelectric layer reached a maximum ?′/?0=4400 at T M≈285 K (f=100 kHz). The narrow peak in the temperature dependence of the dielectric loss tangent for the Ba0.75Sr0.25TiO3 ferroelectric layer, observed for T<T M, shifted toward lower temperatures with decreasing frequency and increasing bias voltage applied to the electrodes. 相似文献