共查询到19条相似文献,搜索用时 562 毫秒
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本文解释了La2CuO4+δ(0≤δ≤0.09)和La2-xSrxCuO4(0≤x≤0.3)两种p型系统含铜稀土氧化物中的电阻和Seebeck系数与温度的依赖关系,在室温以上,一氧大气压下的La2CuO4+δ系统趋于失氧;在500 K以上,超导样品显示出失氧的一级相变,并且恢复到反铁磁相。在转变温度T1≈300 K以下,对0<δ<0.05成份的样品,相分离成反铁磁相和超导相;而在Tcρ≈100 K的温度范围内,超导相进一步分离成富空穴和贫空穴畴。在0.04≤δ≤0.09范围内,Tc处的电阻陡降出现了台阶;我们认为,它反映了电子成对的起伏。在La2-xSrxCuO4系统中,对于成分为01≈300 K以上,空穴的运动是弥散的,但是ΔHm=0;而对于x≥0.22的样品,经历了从平滑到Fermi液态的转变。成份为0c1范围(其中空穴继续以弥散方式运动)是亚稳的,但是,在Tcρ≤150 K范围,出现了电荷起伏。当样品冷却通过T1时,对于成份为0.15≤x≤0.2的样品,经历了由弥散到强质量增强巡游电子状态的转变;在Tc处,从均匀的修饰电子的正常态凝聚成超导的载流子对。在超导成份样品的正常态中,不寻常的电子-晶格相互作用,可以归结为在CuO2面上从更离子性的到共价性的Cu:3dx2-r2─O:Pσ键合的转变;通过这种转变,轨道杂化和Hubbard U参量随Cu─O键长和Cu原子上的外表局域氧化态都产生灵敏的变化。 相似文献
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本文采用超高氧压2.3 GPa合成方法,得到超导相含量大于30%的超导化合物La2CuO4+δ所采用的压力是目前所见报导中对La2CuO4化合物施加的最高氧压。湿化学方法测量给出过量氧含量δ=0.05±0.01,而TGA(氮气中)给出δ=0.143。高氧压合成产物经在空气中、不同温度下加热,然后淬火到室温,结果发现超导体在200~300 ℃的加热处理中存在着一个一级相变。经此相变后,超导体转变成反铁磁半导体。TGA及DSC证实了此相变的存在。该相变前后所联系的氧含量变化恰好为湿化学方法给出的结果,这部分与超导电性存在联系的过量氧,实际上引起了Cu2+向Cu(2+2δ)+的转变。该结果强有力地排除了所谓“超氧化物”引起超导电性的可能性。 相似文献
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采用金刚石压砧高压装置,研究了双钙态矿结构化合物Sr2FeNbO6及其掺杂物Sr2FeMo0.3Nb0.7O6在室温下,20 GPa内电阻和电容随压力的变化,并发现Sr2FeNbO6在7.5 GPa左右压力下发生了相变,而Sr2FeMo0.3Nb0.7O6的相变发生在2.8 GPa左右。并结合这两个样品的高压下的同步辐射能散X射线衍射实验,进一步证明了这两种相变是电子结构相变引起的。 相似文献
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本文用超声相比较方法测定了高Tc超导体La1.85Sr0.15CuO4,La2CuO4和YBa2Cu3O7的纵波和横波声速,进而导出了它们的纵向模量、切变模量、杨氏模量、泊松比、德拜温度及定体比热。在La1.85Sr0.15CuO4样品上,还进行了压力实验,发现所有弹性模量都是随压强增加而增加。定体比热cV和泊松比σ在高压下则略有下降。德拜温度是随压强增加而增加的。 相似文献
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以反滴共沉定法制备了NiFe2O4纳米微粉,并在不同压力下将其压制成纳成米固体,然后用XRD谱和ESR谱研究了NiFe2O4纳米固体结构和界百状态随压制压力的变化。实验结果表明,NiFe2O4纳米固体的结构在高压下没有明显的变化,但其ESR谱的共振线宽和g因子值随着压力升高均表示出先逐渐增大至最大值,然手缓慢下降的规律。这种变化可以归因于纳米固体内部界面离子间的磁相互作用在压力的下所发生和变化。这引起实验结果境示,对于NiFe2O4纳米固体而言,最佳的成型压力是4.5 GPa,在此压力下,NiFe2O4纳米粒子既可以被压制成致密的纳米固体,又能够保留下它们的纳米结构和纳米性质。 相似文献
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Hinrichsen B Dinnebier RE Rajiv P Hanfland M Grzechnik A Jansen M 《J Phys Condens Matter》2006,18(25):S1021-S1037
Methods have been developed to facilitate the data analysis of multiple two-dimensional powder diffraction images. These include, among others, automatic detection and calibration of Debye-Scherrer ellipses using pattern recognition techniques, and signal filtering employing established statistical procedures like fractile statistics.All algorithms are implemented in the freely available program package Powder3D developed for the evaluation and graphical presentation of large powder diffraction data sets.As a case study, we report the pressure dependence of the crystal structure of iron antimony oxide FeSb(2)O(4) (p≤21?GPa, T = 298?K) using high-resolution angle dispersive x-ray powder diffraction. FeSb(2)O(4) shows two phase transitions in the measured pressure range. The crystal structures of all modifications consist of frameworks of Fe(2+)O(6) octahedra and irregular Sb(3+)O(4) polyhedra. At ambient conditions, FeSb(2)O(4) crystallizes in space group P4(2)/mbc (phase I). Between p = 3.2?GPa and 4.1?GPa it exhibits a displacive second order phase transition to a structure of space group P 2(1)/c (phase II, a = 5.7792(4)??, b = 8.3134(9)??, c = 8.4545(11)??, β = 91.879(10)°, at p = 4.2?GPa). A second phase transition occurs between p = 6.4?GPa and 7.4?GPa to a structure of space group P4(2)/m (phase III, a = 7.8498(4)??, c = 5.7452(5)??, at p = 10.5?GPa). A nonlinear compression behaviour over the entire pressure range is observed, which can be described by three Vinet equations in the ranges from p = 0.52?GPa to p = 3.12?GPa, p = 4.2?GPa to p = 6.3?GPa and from p = 7.5?GPa to p = 19.8?GPa. The extrapolated bulk moduli of the high-pressure phases were determined to K(0) = 49(2)?GPa for phase I, K(0) = 27(3)?GPa for phase II and K(0) = 45(2)?GPa for phase III. The crystal structures of all phases are refined against x-ray powder data measured at several pressures between p = 0.52?GPa, and 10.5?GPa. 相似文献
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分析并讨论了La_(1.6-x)Nd_(0.4)Sr_x CuO_4系列单相性样品(x=0.08~0.25)的晶体结构和超导电性。结果表明,晶体结构随着Sr掺杂量的变化规律与La_(2-x)Sr_x CuO_4系列相似。超导电性方面,La_(1.6-x)Nd_(0.4)Sr_x CuO_4系列超导转变温度均远小于相应的La_(2-x)Sr_xCuO_4系列组分。同La_(1.875)Ba_(0.125)CuO_4相似,La_(1.48)Nd_(0.4)Sr_(0.12)CuO_4处出现显著的极小值8K但高于La_(1.875)Ba_(0.125)CuO_4。La_(1.6-x)Nd_(0.4)Sr_x CuO_4系列的超导电性明显与La_(2-x)Sr_x CuO_4系列有着不同的特性,虽然同La_(2-x) Ba_xCuO_4系列相似但仍有区别。我们从其晶体结构的反常变化的角度对La_(1.6-x)Nd_(0.4)Sr_x CuO_4系列反常的超导电性做了初步的解释。 相似文献
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Friedrich A Biehler J Morgenroth W Wiehl L Winkler B Hanfland M Tolkiehn M Burianek M Mühlberg M 《J Phys Condens Matter》2012,24(14):145401
The high-pressure behaviour of Bi2Fe4O9 was analysed by in situ powder and single-crystal x-ray diffraction and Raman spectroscopy. Pressures up to 34.3(8) GPa were generated using the diamond anvil cell technique. A reversible phase transition is observed at approximately 6.89(6) GPa and the high-pressure structure is stable up to 26.3(1) GPa. At higher pressures the onset of amorphization is observed. The crystal structures were refined from single-crystal data at ambient pressure and pressures of 4.49(2), 6.46(2), 7.26(2) and 9.4(1) GPa. The high-pressure structure is isotypic to the high-pressure structure of Bi2Ga4O9. The lower phase transition pressure of Bi2Fe4O9 with respect to that of Bi2Ga4O9 (16 GPa) confirms the previously proposed strong influence of cation substitution on the high-pressure stability and the misfit of Ga3+ and Fe3+ in tetrahedral coordination at high pressure. A fit of a second-order Birch–Murnaghan equation of state to the p–V data results in K0 = 74(3) GPa for the low-pressure phase and K0 = 79(2) GPa for the high-pressure phase. The mode Grüneisen parameters were obtained from Raman-spectroscopic measurements. 相似文献
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We report the first in situ boron K-edge inelastic x-ray scattering (IXS) spectra for alkali borate glasses (Li2B4O7) at high pressure up to 30 GPa where pressure-induced coordination transformation from three-coordinated to four-coordinated boron was directly probed. Coordination transformation (reversible upon decompression) begins around 5 GPa and the fraction of four-coordinated boron increases with pressure from about 50% (at 1 atm) to more than 95% (at 30 GPa) with multiple densification mechanisms, evidenced by three distinct pressure ranges for (d[4]B/dP)T. The lithium K-edge IXS spectrum for Li-borate glasses at 5 GPa shows IXS features similar to that at 1 atm, suggesting that the Li environment does not change much with pressure up to 5 GPa. These results provide improved understanding of the structure of low-z glass at high pressure. 相似文献
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本文采用DAC(金刚石压砧高压腔)装置,对氧化镍进行了静水压、非静水压、电导率测量等系统高压实验,获取了氧化镍等温压缩、高压相变及电导率压力效应的新结果,并在实验数据的基础上,对其高压相变与电性及磁性变化关系及体弹性模量作了分析讨论。 相似文献
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Cuk T Struzhkin VV Devereaux TP Goncharov AF Kendziora CA Eisaki H Mao HK Shen ZX 《Physical review letters》2008,100(21):217003
We report pressure-tuned Raman and x-ray diffraction data of Bi(1.98.)Sr(2.06)Y(0.68)Cu(2)O(8+delta) revealing a critical pressure at 21 GPa with anomalies in electronic Raman background, electron-phonon coupling lambda, spectral weight transfer, density dependent behavior of phonons and magnons, and a compressibility change in the c axis. For the first time in a cuprate, mobile charge carriers, lattice, and magnetism all show anomalies at a distinct critical pressure in the same experimental setting. Furthermore, the spectral changes suggest that the critical pressure at 21 GPa is related to the critical point at optimal doping. 相似文献