共查询到19条相似文献,搜索用时 656 毫秒
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用第一原理的LDF-LMTO-ASA超元胞法,模拟由X射线吸收谱精细结构测定的BaBiO3中,Bi有两种价态Bi3+和Bi5+及与之相应的两种不同键长的Bi—O八面体,以及K掺杂对晶体结构的影响.计算了Ba4Bi4O12,(Ba3K)Bi4O12,(BaK)Bi2O6,(BaK3)Bi4O12,K2Bi2O6(简记为(404),(314),(112),(134),(022))五种“样本”的电子结构.结果表明,(404)和(314)分别为Eg=1.6eV及Eg=1.5eV的半导体,其它“样本”为金属.总能的分析表明(134)是不稳定的,故溶解极限为x=0.5.以“取样”方式按伯努利分布确定任意组分各“样本”的概率,进而计算了(Ba1-xKx)BiO3电子结构随组分的变化.最后用逾渗模型说明了超导转变温度Tc在x=0.25附近的突变
关键词: 相似文献
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报道在超声射流冷却条件下用同步辐射VUV光源研究CH2Br2的振动自电离结构.根据测量的105—123nm范围内母体离子(CH2Br2+)的光电离产率曲线,获得CH2Br2的绝热电离势为10.23±0.01eV.CH2Br2+的最低三个电子激发态,即A(2A2),B(2B1),C(2A1)分别位于10.78±0.01eV,11.20±0.01eV和11.27±0.01eV.在115.01—121.15nm范围内,观察到CH2Br2自电离峰叠加在若干台阶结构上,台阶平均宽度为716.8±40.0cm-1,对应于CH2Br2+(X2B2)中Br-C-Br反对称的伸缩振动(v9),所有的峰均归属为收敛于CH2Br2+(X2B2,v+)振动能级的ns,np和nd自电离Rydberg态.此外,对CH2Br2光解离电离产生离子型自由基CH2Br+(X)的光电离产率曲线的结构也进行了归属
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在较宽的温度(4.2-80K)和磁场(0-8T)范围内测量了YBa2Cu3O7-δ和Y0.9Eu0.1Ba2·Cu3O7-δ样品的磁滞回线和磁弛豫,研究了其M(t),Jc(T)和Ueff(J)关系,并与现有的一些理论模型所预言的结果进行了比较。结果表明:(1)与YBa2Cu3O7-δ相比,Y0.9Eu0.1·Ba2Cu3O7-δ样品的有效钉扎势和无磁通蠕动时的临界电流密度有明显提高,表明Eu的部分替代引入了新的、具有更大的钉扎势的钉扎中心;(2)与其它模型相比,集体钉扎——蠕动理论对我们的实验结果作了更好的描述,因而本文为这一理论提供了新的实验证据。
关键词: 相似文献
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研究了Gd1-xCaxBa2Cu3O7-y(0.0≤X≤0.20)高温超导体在常压和高压下的超导电性在1-300K温度范围内,利用Bridgman对顶砧获得压力达9.0GPa,测量了(X=0.10,0.15,0.20)样品的dTc/dp分别为7.68,7.8和4.46K/GPa。发现Tc的压力导数随着ca2+含量的增加而下降,分析了氧含量对Tc和dTc/dP的影响.利用常压下晶格参数精修值和阳离子与氧离子间距随压力的改变,说明CuO2面在超导电性上的作用,用CuO2面之间耦合解释Tc(P)曲线的非线性关系。
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La/Mn co-doped Bi4Ti3O12 ceramics,Bi3.25La0.75Ti3-xMnxO12(x=0.02,0.04,0.06,0.08),were prepared by the solid-state reaction method.The influence of manganese substitution for the titanium part in Bi 3.25 La 0.75 Ti 3 O 12 on the sintering behaviour,microstructure,Raman spectra and electrical properties was investigated.The experimental results show that the phase composition of all samples with and without manganese doping,sintered at 1000 ℃,consists of a single phase with a bismuth-layered structure belonging to the crystalline phase Bi4Ti3O12.There is no evidence of any impurity phase,but a small change in crystallographic orientation is observed.The Curie temperature of Bi3.25La0.75Ti3-xMnxO12 ceramics is steadily shifted to lower temperature with increasing Mn-doping content.Moreover,the remnant polarisation(Pr) of Bi3.25La0.75Ti2.92Mn0.08O12 samples increases with Mn-doping content,and the Bi3.25La0.75Ti2.92Mn0.08O12 sample exhibits the largest P r of 16.6 μC/cm 2. 相似文献
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We have observed the anomalous temperature dependence of the phonon modes in the Raman spectra of Bi2Ti4O11 and the modified Bi2Ti4O11 with the dopant of PbO. The square of the lowest mode frequency in both substances decreases linearly with increasing temperature, while the damping constant increases reaching a peak value at the transition temperature. The mode frequency, however, does not tend to zero but stays finite and the damping constant decreases above the transition temperature. The mode is Raman-active both above and below the transition temperature. 相似文献
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We present an effective way in this paper to increase the density of lanthanum doped bismuth titanate ceramics, Bi4-xLaxTi3O12 (BLT), thereby significantly improving the performance of the BLT ceramics. Dense BLT ceramicses, Bi4-xLaxTi3O12 (x = 0.25, 0.5, 0.75, 1.0), are prepared by using nanocrystalline powders fabricated by a-gel method and high-pressure technique. The microstructures of the BLT ceramicses prepared separately by conventional-pressure and high-pressure techniques are investigated by using x-ray diffraction and transmission electron microscope. The influence of La-doping on the densification of bismuth titanate ceramics is investigated. The experimental results indicate that the phase compositions of all samples with various lanthanum dopings sintered at 900°C possess layer-structure of Bi4Ti3O12 . The green compacts are pressed under 2.5 GPa, 3.0 GPa, 3.5 GPa and 4.0 GPa, separately. It is found that the density of BLT ceramics is significantly increased due to the decreasing of porosity in the green compacts by high-pressure process. 相似文献
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R.Z. Hou 《Solid State Communications》2004,130(7):469-472
Ceramics with the nominal composition of SrBi4−xLaxTi4O15 have been prepared within the range of 0≤x≤1.8, and the dielectric properties are investigated. Single phase SrBi4−xLaxTi4O15 solid solution exists until the secondary phase of La2/3TiO3 appears at x=1.6. The Curie temperature is 520 °C for pure SrBi4Ti4O15, and it shifts to low temperature with increasing x, which is due to the smaller structural distortion caused by La3+ substitution. In addition, the dielectric constant anomaly is suppressed with the substitution. No dielectric relaxation behavior is observed. When x≥1.2, the paraelectric state is attained in the present ceramics. La3+ substitution effects on the SrBi4Ti4O15 ceramics are also compared with the previous work on Bi4−xLaxTi3O12. 相似文献
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This paper reports that La-doped BiFeO 3(Bi1-x La x FeO3,x = 0,0.1,0.2,0.3,0.6,0.8 and 1.0) were studied by using micro-Raman spectroscopy and x-ray diffraction(XRD).The XRD patterns indicate that the structure of Bi1-xLaxFeO 3 changes from rhombohedral BiFeO3 to orthorhombic LaFeO3.The results of Raman spectroscopy show good agreement with the XRD results.Strikingly,the phonon peak at around 610 cm-1 and the two-phonon peaks in the high frequency range exist in all compounds and enhance with increasing La substitution.The increasing intensity of the 610 cm-1 peak is attributed to the changes in the FeO 6 octahedron during the rhombohedral-orthorhombic phase transition.The enhancements of the two-phonon peaks are associated with the breakdown of the cycloid spin configuration with the appearance of the orthorhombic structure.These results indicate the existence of strong spin-phonon coupling in Bi1-xLax FeO3,which may provide useful information for understanding the effects of La content on the structural and magnetic properties of Bi1-xLaxFeO3. 相似文献
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采用固相烧结工艺,制备了不同La掺杂量(x=0.00,0.25,0.50,0.75,1.00,1.25和1.50) 的(Bi, La)4Ti3O12-Sr(Bi, La)4Ti4O15 (SrBi8-xLaxT i7O27)共生结构铁电陶瓷样品.用x射线衍射对其进行微结构分析 ,并测量铁
关键词:
4Ti3O12-SrBi4Ti4 O15')" href="#">Bi4Ti3O12-SrBi4Ti4O15
La掺杂
铁电性能
居里温度
弛豫铁电 相似文献
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按x=0.00,0.10,0.25,0.50,0.75和1.00,采用固相烧结工艺,制备了不同La掺杂量的SrBi4-xLaxTi4O15的陶瓷样品. 用x射线衍射对其微结构进行了分析,并测量了铁电、介电性能.结果发现,La掺杂未改变SrBi4Ti 4O15的晶体结构.随掺杂量的增加,样品的矫顽场(Ec)下降,剩余极化(2P关键词:
4-xLaxTi4O15')" href="#">SrBi4-xLaxTi4O15
La掺杂
铁电性能
相变温度
弛豫铁电 相似文献