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分别测量高 T_c(2223相)BSCCO 银包套超导带的交流磁化率实部 X′-T 和虚部 X″-T 曲线与交流场振幅的关系,其虚部损耗峰高度及对应的温度随交流场振幅增加分别有上升和下降的趋势.当磁场垂直样品 c 轴(平行样品 c 轴)时,损耗峰的移动幅度小于平行时的移动. 相似文献
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本文研究了在真空、空气和氧气中烧结制备的三种 CaCu3Ti4O12陶瓷材料的介电特性. 交流阻抗测量结果表明在10—300 K温度范围, 三种样品的介电温谱中均出现三个平台, 其电阻实部和电容虚部在相应温度出现损耗峰, 真空条件烧结的样品具有较高的介电平台和较明显的电阻实部与电容虚部峰值, 表明氧含量和氧空位对CaCu3Ti4O12的介电性质具有重要影响, 介电温谱出现的三个平台分别源于晶粒、晶界及氧空位陷阱.温谱分析表明晶粒的激活能与烧结气氛有较大关系,氧空位引起的电子短程跳跃及跳跃产生的极化子是晶粒电导和电容的主要起源.氧空位陷阱的激活能基本与烧结气氛无关,约为0.46 eV. 氧空位对载流子的陷阱作用是CaCu3Ti4O12 低频高介电常数的重要起源. 相似文献
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本文研究了 Bi_2Sr_2CaCu_2O_y,单晶在磁场 H 垂直于 c 轴情况下的交流磁化率,得到了交流磁化率虚部峰温度 T_p 和外加直流磁场 H_(DC)的关系为:(1-T_P/T_c)∝H_(DC)~(0.2).本文还对不可逆线进行了讨论,并和用其他方法测量的不可逆线作了比较. 相似文献
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利用瓦特计技术,研究了YBa_2Cu_3O_(7-y)烧结样品和粉末熔化法(PMP)织构样品在77K和50Hz交变磁场下的交流(ac)损耗(?)实验结果表明,ac损耗(?)同外磁场振幅H_m之间遵从幂函数规律:(?)∝H_m~n对于YBa_2Cu_3O_(7-y)的烧结样品:(1)当H_m<40Oe时,这样低的磁场已穿透弱连接的晶粒边界网络,导至晶粒间的损耗,(?)∝H_m~(1.6)(2)当40Oe≤H_m<170Oe时,中等磁场破坏了晶粒间的耦合,并且磁通穿进了晶粒内,引起不完全穿透的晶粒内损耗,(?
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由于铁磁性样品的交流磁化率虚部χ″随磁场强度H的变化是非线性的,在低场(0~12 mT)有一个与铁磁共振信号强度相当的低场非共振信号. 利用ESR谱仪测量交流磁化率虚部χ″对磁场强度H的一次微分随磁场强度的变化dχ″/dH~H,研究Fe84Zr3.5Nb3.5B8Cu1合金薄带的动态磁化特性. 合金薄带样品是各向异性的,易磁化轴(易轴)在薄带的横向方向,外加磁场H在易轴方向. 样品在可逆磁化区域(0~2.0 mT)和趋近饱和的磁化区域(9.0 mT以上),dχ″/dH=0;在不可逆畴壁移动过程中,当H为4.2 mT 时, χ″(H)达到最大值χmax;在磁畴转动过程中,χ″(H)正比于H2(瑞利区);而实验中却发现,在某些区域交流磁化率虚部χ″(H) 与磁场强度H的n次方即Hn(n≥3)有关;而且发现,在一定区域,有三段不可逆畴壁移动和磁畴转动交替出现的现象. 在这一过程中,dχ″/dH为常数的磁场范围分别为4.8~5.2mT, 5.8~6.4 mT, 8.0~8.5 mT, 其常数相对值分别为1:0.85:0.60. 样品的交流磁化率虚部χ″对磁场H的微分dχ″/dH随磁场H的这一变化规律反映了不可逆畴壁移动和磁畴转动交替发生的微观过程. 相似文献
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本介绍如何利用交流磁化率测量高温超导体与电流密度J,直流场Hd和温度T有关的磙通钉能U。根据磁通扩散理论和随外场变化的交流磁化率虚部x峰温的系统实验研究,就可以得到上述能量函数,对掺Pb和Ba的TlSr2Ca2Cu3Oy超导体的系统交流磁化率的测量和分析得到的结果U。 相似文献
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Effects of Zr substitution on structural,morphological, and magnetic properties of bismuth iron oxide phases 下载免费PDF全文
The present study involves co-precipitation method to grow un-doped and Zr-doped bismuth iron oxide with x_(Zr)=0.10–0.30. The molar solutions of ferric chloride(FeCl_3), zirconyle chloride(ZrOCl_2), and bismuth chloride(BiCl_3) are prepared in distilled water, and are allowed to react with sodium hydroxide(Na OH). The synthesized powders are then converted into pellets, which are sintered at 500℃ for two hours in a muffle furnace. X-ray diffraction(XRD) shows multi-phase formation in un-doped and Zr doped samples. Scanning electron microscope(SEM) depicts layered structure at low Zr concentration x_(Zr)= 0.10, while uniform surface with smaller grains and voids is observed at x_(Zr)= 0.20, but at x_(Zr)= 0.30, cracks and voids become prominent. The ferromagnetic nature of the un-doped sample is observed by vibrating sample magnetometer(VSM), while paramagnetic behavior appears due to Zr doping. The ferromagnetism in un-doped sample is lost by Zr doping, which is due to the formation of additional Fe–O–Zr bonds that induce paramagnetic behavior. 相似文献
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Yingfan Xu Guangzhao Pan Zhenhong Mai Changqin Jin Daoyang Dai Wenkui Wang 《Physica C: Superconductivity and its Applications》1992,200(3-4):242-250
The microstructure of Nd1.85Ce0.15CuO4−y superconductor sintered under high pressure and ambient pressure has been characterized by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HREM). It has been observed that the conventional sample is porous, while the high-pressure sample is almost pore-free. It is confirmed that the thermal treatment under high pressure recovers fairly well connections between grains which were partly crushed during the compression process; hence the weak links at grain boundary are improved. Furthermore, a high density of defects induced by pressure is observed in the high-pressure sample. In contrast, the conventional sample is nearly perfect. For comparison, the microstructure of a sample pressed at high pressure at room temperature is also examined. The influence of pressure on the microstructure and the superconductivity is discussed. 相似文献
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采用X射线衍射(XRD)分析、扫描电子显微镜(SEM)和能谱分析(EDX)等方法,对在压力5.6 GPa、温度1 460 ℃条件下,加热时间分别为2、3、4、6、8、10 min的聚晶金刚石复合片(PDC)样品进行了分析。结果表明:PDC的烧结经历了金刚石的石墨化过程,而且在烧结过程中金刚石层表面的XRD图谱出现了WC衍射峰,强度由弱到强,再由强到弱,直至消失;进一步的研究发现,PDC中助烧结剂Co的晶格常数因C和W原子的固溶会变大,并随PDC加热时间的延长出现一个峰值;从硬质合金基体扩散到金刚石层的Co由于扩散通道各异、所受阻力不同,使得其分布不均匀。 相似文献
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MOCVD生长的GaN和GaN:Mg薄膜的拉曼散射 总被引:2,自引:1,他引:1
通过显微拉曼散射对用金属有机化学气相沉积(MOCVD)法在Al2O3衬底上生长的六方相CaN和掺Mg的P型GaN薄膜进行了研究。在两个样品的拉曼散射谱中同时观察到位于640,660cm^-1附近的两个峰。640cm^-1的峰归因于布里渊区边界(L点)最高声学声子的二倍频,而660cm^-1的峰为布里渊区边界的光学声子支或缺陷诱导的局域振动模。掺Mg的GaN在该处的峰型变宽是Mg诱导的缺陷引起的加宽或Mg的局域模与上述两峰叠加的结果。在掺Mg的样品中还观察到276,376cm^-1几个局域模并给予了解释。同时掺Mg的GaN中出现了应力弛豫的现象,掺Mg引起的失配位错和电子-声子相互作用都有可能对E2模的频率产生影响。 相似文献
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Shyam Surthi Sushma Kotru R.K. PandeyPatrick Fournier 《Solid State Communications》2003,125(2):107-110
Polycrystalline samples of La0.67Ca0.33MnO3 were prepared by solid-state reactions by varying the pelletization force and the sintering temperature. Lowering the sintering temperature gave rise to smaller grains and increased the overall resistivity of the ceramic. Partial melting was observed in the ceramics sintered at higher temperatures (1400-1500 °C). Additionally, these ceramics showed two distinct resistivity peaks. The resistivity peak near the magnetic transition (TC) was sharp, whereas the second peak was a broad one observed below TC. 相似文献
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Investigation of the domain structure of sintered Nd-Fe-B permanent magnets by Bitter-pattern method
Witold Szmaja 《Czechoslovak Journal of Physics》2004,54(12):1503-1509
The conventional Bitter-pattern technique and the colloid-scanning electron microscopy (colloid-SEM) method were used to study
the domain structure of polycrystalline sintered Nd-Fe-B permanent magnets. In the thermally demagnetized state most of the
grains are multidomain and the domain structures resemble those observed in bulk uniaxial crystals with strong magnetocrystalline
anisotropy. Investigations of the magnetic microstructure during magnetizing cycle showed that the domain walls can easily
be moved within the grains and that the magnetization reversal in sintered Nd-Fe-B magnets occurs predominantly by the nucleation
and expansion of reverse domains at structural imperfections near the grain boundaries. It is also shown that the colloid-SEM
method is more surface sensitive and reveals the domain structure with better resolution than the conventional Bitter technique.
Thanks to the application of digital image processing systems, clear and high contrast domain images were obtained.
The work was supported by the Lódź University within Research Grant 505/694 (2004). 相似文献
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The microstructure of WC-Co composites sintered with VC or with a mixture of VC and Cr3C2 is investigated by several techniques in order to understand the grain growth inhibition process. In this work, using the high-resolution transmission electron microscopy and high-resolution energy-filtering electron microscopy, we are able to study on the atomic scale the microstructure and composition of the phases present in the alloys. A thin (VW)C x layer less than 1 nm thick covering all surfaces of WC grains and thin (VW)C x platelets embedded in the WC grains are evidenced. Microsteps are observed at the interface between Co and WC along the ?11amp;2macr;0?WC directions. Small (VW)C x precipitates lie on the (0001)WC and {10amp;1macr;0} facets of these steps. On the (0001) surface of WC grains, other stacking sequences of the metal planes are sometimes observed and, in particular, the occurrence of the compound (VW)2C is shown. Owing to these observations a grain growth inhibition mechanism is proposed. 相似文献
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利用水热法合成了Bi2Te3纳米粉末, 并在300–500 ℃的温度范围内对其进行等离子烧结. X射线衍射测试表明制得的Bi2Te3粉末是单相的. 对于300–500 ℃范围内烧结的样品, 扫描电子显微镜观察发现随着烧结温度的升高样品颗粒明显增大, 但是根据X射线衍射峰的宽度计算得到的样品晶粒大小并没有明显的变化. 正电子湮没寿命测试结果表明, 所有的样品中均存在空位型缺陷, 而这些缺陷很可能存在于晶界处. 正电子平均寿命随着烧结温度的升高而单调下降, 说明较高的烧结温度导致了空位型缺陷浓度的降低. 另外, 随着烧结温度从300 ℃升高到500 ℃, 样品的热导率从0.3 W·m-1·K-1升高到了2.4 W·m-1·K-1, 这表明在纳米Bi2Te3中, 空位型缺陷和热导率之间存在着密切的联系. 相似文献