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本文研究了c轴取向的Hg0.9Tl0.1Ba2Ca2Cu3O8+δ超导膜(Tc〉124K)在混合态下的电阻展宽及霍尔效应。低电阻区域的展宽显示出热激活磁通蠕动行为。在膜的超导转变温度以下,我们观察到霍尔电阻率符号反常现象。霍尔电阻率(ρxy)和纵向电阻率(ρxx)具有ρxy(T)=kρxx^β(T)的标度关系。 相似文献
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实验研究了高温超导体Hg0.9Tl0.2Ba2Ca2Cu3O8+δ的低温热导率与温度和磁场的关系,测量温度为7-20 K,外加磁场为0-6 T.结果表明,在不同外场下,超导体的热导率在实验温区内随温度的增加均单调增加;在固定的温度下外加磁场使超导体的热导率减小,并随外磁场的增加达到一个稳定值;热导的相对变化率κ(H)/κ(0)与磁场的关系以及热导率达到稳定值的磁场与测量温度有关.分析讨论了超导体中正常态电子在磁场下受磁通涡旋散射产生附加的热阻. 相似文献
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我们曾用离子注入法,脉冲激光沉积等方法制备出了HgBa2Ca2Cu3O8+δ超导薄膜.但这些方法费用昂贵,难度较大.因此我们探索利用化学雾化技术在衬底上制备HgBa2Ca2Cu3O8+δ超导薄膜.制备过程包括两个步骤:第一步控制衬底温度制备Ba-Ca-Cu-O薄膜,并退火得到Ba-Ca-Cu-O前驱物;第二步,控制衬底温度并将HgCl2喷射在Ba-Ca-Cu-O前驱物薄膜上得到Hg-Ba-Ca-Cu-O薄膜,并将所得薄膜在氧气中氧化.目前我们正在探索利用这一技术来制备Hg-1223高质量的超导薄膜. 相似文献
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在Tl2Ba2Can-1CunO2n 4(n=1,2,3,4)系列超导性氧化物中,Tl2Ba2Ca2Cu3O10具有最高Tc值(125 K).利用电介质的平均能带模型计算了Tl2Ba2Ca2Cu3O10的局域化学键参数,得到Cu(1)-O键的共价性为0.561,Cu(2)-O键的平均共价性为0.296.应用化学环境因子计算了57Fe在Tl2Ba2Ca2Cu3O10中的穆斯堡尔同质异能位移,证实了57Fe在低掺杂时以Fe3 和Fe4 离子形式占据Cu(1)位置,而在高掺杂时以Fe3 和Fe4 离子形式分别占据Cu(1)和Cu(2)位置.结果表明,化学键理论计算有助于复杂晶体的穆斯堡尔谱的正确分析. 相似文献
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研究了Tl2Ba2CaCu2O8+δ/LaAlO3单晶薄膜的ab平面内电子在超导凝聚过程中的行为,薄膜厚度为3000,转变温度Tc=96K。在凝聚过程中,阻抗谱z(ω,T0)变化剧烈。谱线随温度的变化规律与浅超导区直流压制下的阻抗谱极为相似。随着超导凝聚的加强,谱重从高频区进一步向低频区转移并且导致直流极限下的发散。通过分析,得出超导相变对应了超流电子岛从出现到扩大并最终连成整片超导大陆这样的过程。我们还测试了薄膜载流下的阻抗谱z(ω,B0),观测到临界电流密度随着超导凝聚的进行而增大。 相似文献
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铁电/超导(Ba, Sr)TiO3/YBa2Cu3O7-δ异质结在可调谐微波器件方面具有非常好的应用前景.我们采用1.2°斜切LaAlO3基片,以脉冲激光沉积法(PLD)制备出性能较好的Ba0.1Sr0.9TiO3/YBa2Cu3O7-δ (BST/YBCO)异质薄膜.并进一步研究了YBCO薄膜厚度对BST性能的影响.研究发现当YBCO薄膜厚度增加到180nm附近时,其生长模式由二维step-flow转变为三维岛状模式,严重损害了在YBCO上面生长的BST薄膜的介电性能.具体表现在:BST薄膜的介电常数和可调谐率明显降低,介电损耗和漏电流却大幅度上升.通过测量电容与温度的关系,以应力效应模型对这一实验现象作出解释,认为YBCO薄膜厚度超过临界值,生长模式的转变促使晶格失配应力在YBCO和BST薄膜中得到释放,这导致BST/YBCO界面粗糙,以及BST薄膜中产生了大量的位错和缺陷,BST薄膜的性能因而大为降低.此外,通过对完全相同条件生长的单层YBCO薄膜的表面形貌进行了AFM研究,测试结果进一步验证了YBCO薄膜厚度增加到180nm时,其表面变得异常粗糙,均方根粗糙度(RMS)从120nm厚度时的3nm增加到180nm厚度时的9nm.因此,我们提出:通过严格控制底层YBCO薄膜的厚度,进而控制它的生长模式,能够非常有效地提高BST薄膜的介电性能. 相似文献
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用稀土氧化物硫化法合成了固溶体发光材料(Y0.9Gd0.1)2O2S:Tb和(Gd0.9La0.1)2O2S:Tb,并且用阴极射线和254nm紫外线两种激发方式测试了它们的发光性能.研究了固溶体(Y0.9Gd0.1)2O2S:Tb和(Gd0.9La0.1)2O2S:Tb中Tb3+离子5D3——7FJ和5D4——7FJ的能级跃迁强度随Tb3+离子浓度而变化的关系,以及它们的发光色度随激活剂Tb3+离子浓度的变化,探讨了Tb3+离子的浓度猝灭机理. 相似文献
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用固相反应法制备、并通过没条件的热处理得到了一组同氧含量的Nd0.9Cd0.1ba2Cu3O6+x样品。用X射线衍射确定了样品的相结构。随着氧含量的增大,结构发生从四方到正交相变。进一步用红外吸收谱研究了体系的结构变化特征。谱图上642cm^-1,578cm^-1,538cm^-1峰的出现及位移,与氧含量引起的结构变化是一致的,并讨论结构与超导电性的关系。 相似文献
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Mirzadeh M. Akhavan M. 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,43(3):305-318
We have studied the structural, electrical, and magnetic properties of the
normal and superconducting states Gd(Ba2-xLax)Cu3O7+
[Gd(BaLa)123] samples with 0.0 x 0.8 prepared by the
standard solid-state reaction. XRD characterization shows an
orthorhombic-tetragonal structural transition at x=0.2. Iodometric titration
analysis shows the oxygen content of the samples increase with the increase
of La doping. The resistivity curves show that for x0.15, there is
metallic behavior, and for x0.2, there is a gradual insulating
transition behavior in the normal state. The metal-insulator and
superconductor-insulator transitions occur between x=0.35 and x=0.4. The
superconducting transition temperature decreases with the increase of La
content as two-step curve. The normal-state resistivity is fitted for two
and three dimensional variable range hopping (2D&3D-VRH) and Coulomb gap
(CG) regimes, separately. The results show that the dominant mechanism is CG
for x0.35, and VRH for x0.4. The pinning energy U, derived from
the thermally activated flux creep (TAFC) model and Ambegaokar-Halperin (AH)
theory, shows a power-law relation as UH -. The
critical current density decreases with the increase of La doping and
magnetic field. The E-J curves show that the induced electric field
increases with the increase of magnetic field and La concentration. The
magnetization measurements indicate that the critical penetration fields and
magnetic current density decrease with La doping. 相似文献
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ELECTRONIC STRUCTURE OF Hg0.8Pb0.2Ba2Ca2Cu3O8+δ: THE ROLE OF Pb DOPING,OXYGEN DOPING AND HIGH PRESSURE 下载免费PDF全文
The effects of Pb doping, oxygen doping ($\delta$= 0.1,0.2,0.4 and 0.5) and high pressate (4, 8, 15 and 20GPa) on the electronic structure of Hg0.8Pb0.2Ba2Ca2Cu3O8+δ have been examined by the recursion method. Our calculations show that Pb doping only decreases the hole concentration slightly and oxygen doping increases the hole concentration monotonically and significantly as δ varies from 0 to 0.5, with each excess oxygen atom contributing about 1.7 holes to the CuO2 layers. The optimal δ is estimated to be around 0.4, The hole conceatration increases initially with pres-sure but decreases as P > 8GPa (i.e., dn/dP does change sign at ~ 8GPa). The suppressed Tc(P) by Pb substitution has to be described in the modified Neumeier's model. 相似文献
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K. Nagasao T. Masui S. Tajima 《Physica C: Superconductivity and its Applications》2008,468(15-20):1188-1191
Electronic anisotropy was studied for overdoped (Y, Ca)Ba2Cu3O7−δ with various doping levels (p). It was found that the pseudogap-like behavior in the resistivity disappear when p exceeds 0.17, independent of the oxygen deficiency. The anisotropy ratio γ estimated from upper critical fields showed a rapid decrease at around p = 0.18, approaching γ = 3 for p > 0.20. 相似文献
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