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CM Thaker S Rayaprol Krushna Mavani DS Rana MS Sahasrabudhe SI Patil DG Kuberkar 《Pramana》2002,58(5-6):1035-1039
The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO3 perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good
example of these properties is (La1−2x
Pr
x
Ca
x
)MnO3 (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T
c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using
X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for
understanding the structural, transport and magnetic properties are discussed in detail. 相似文献
3.
§ 1.Introduction WearegivenkindependentWishartdensitiesofthe (p +q)× (p +q)randomsymmetricpositivedefinitematricesG1,… ,Gktobeg(Gi) =Kexp -12 trR- 1i Gi Gi12 (ni- q-p- 1) ,(1 )wherei=1 ,… ,k,andRidenotesthepopulationcorrelationmatrixofthei thpopulationandKasagenericletterdenote… 相似文献
4.
Dussauze M Giannoudakos A Velli L Varsamis CP Kompitsas M Kamitsos EI 《The Journal of chemical physics》2007,127(3):034704
Lead-germanate materials are attractive systems for photonics applications. In this context, amorphous lead-germanate films were grown by pulsed-laser deposition at different substrate temperatures and oxygen pressures using a glassy target of composition 0.4PbO-0.6GeO(2). Optical and infrared measurements showed that the substrate temperature has a strong influence on the optical quality and stability of the deposited films. An accurate characterization of films was achieved by comparing experimental and simulated transmittance spectra in the infrared, and allowed to probe the structural evolution and variations in composition as a function of oxygen pressure. The results showed that the difference in reactivity of lead and germanium toward oxygen in the laser-produced plasma allows for composition adjustments in the lead-germanate films by varying the oxygen pressure in the deposition chamber. 相似文献
5.
Molecular dynamics simulations are carried out in xLi2O-(1-x)B2O3 glasses (x=0.2-0.6) at T=1250 K, where cluster size distributions for Li cations and nonbridging oxygen (NBO) atoms are calculated. The existence of percolating clusters above x=0.3 places the percolation threshold between x=0.3 and 0.4 for the system under investigation, which is consistent with the abrupt increase of the diffusion coefficient of Li cations observed at x=0.4. It is also shown that the clusters of Li cations consist mainly of Li atoms found in the vicinity of NBO atoms. This result explains the higher mobility exhibited by this type of cations compared to the mobility of Li cations in the vicinity of bridging oxygen atoms. 相似文献
6.
A. Tsigara L. Velli A. Giannoudakos C.P.E. Varsamis M. Kompitsas N.A. Vainos E.I. Kamitsos 《Applied Physics A: Materials Science & Processing》2004,79(4-6):1319-1321
Lead-germanate glasses of composition xPbO–(1-x)GeO2 (x ranging from 0.1 to 0.4) have been synthesized and used as ablation targets for reactive pulsed laser deposition (PLD) at various oxygen pressures. The bulk glassy materials and the PLD-produced films were investigated by Fourier-transform infrared spectroscopy to reveal the effects of the bulk stoichiometry and of the reactive atmosphere employed for film preparation on the structural characteristics of the studied bulk glasses and thin-film forms. PACS 81.15.Fg; 78.30.-j; 42.70.Ce 相似文献
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S Rayaprol Krushna Mavani CM Thaker DS Rana Keka Chakravorty SK Paranjape M Ramanadham Nilesh A Kulkarni DG Kuberkar 《Pramana》2002,58(5-6):877-880
A new series of mixed oxide superconductors with the stoichiometric composition La2−x
Dy
x
Ca
y
Ba2Cu4+y
O
z
(x=0.0 − 0.5, y=2x) has been studied for structural and superconductiong properties. Our earlier studies on La2−x
(Y/Er)
x
Ca
y
Ba2Cu4+y
O
z
series, show a strong dependence of T
c on hole concentration (p
sh). In the present work, the results of the analysis of the neutron diffraction measurements at room temprerature on x=0.3 and 0.5 samples are reported. It is interesting to know that Ca substitutes for both La and Ba site with concomitant
displacement of La onto Ba site. Superconductivity studies show that maximum T
c is obtained for x=0.5, y=1.0 sample (T
c ∼ 75 K), for La1.5Dy0.5Ca1Ba2Cu5O
z
(La-2125). 相似文献
9.
One hundred and fifty-seven nanometers irradiation of LiF crystals accelerates the penetration of C, O, N, Si and other contaminants within the crystal bulk. New bonding between the contaminant elements in both the irradiated and the non-irradiated areas of the crystal was identified. The chemical changes eventually form inhomogeneous nano/micro-islands, which further agglomerate to larger structures in the form of an interfacial layer. The concentration and diffusion (∼100 nm) of contaminants in the irradiated part of the crystal is higher than for the non-irradiated one. The accelerated diffusion is due to a force perpendicular to the crystal surface. This force is generated by the laser's electric field gradient in the direction of beam propagation due to the inhomogeneous absorption at the interfacial layer. A theoretical diffusion model in the presence of the laser field allows rationalizing and interpreting the experimental results. 相似文献
10.
P. Dore A. Paolone S. Tatoni C. P. Varsamis V. Boffa C. Romeo S. Barbanera F. Murtas 《International Journal of Infrared and Millimeter Waves》1994,15(4):723-738
We measured reflectance spectra R(v) of oxygen deficient Y1Ba2Cu3O7–x (YBCO) films of different thickness, with critical temperatures between 85 and 87 K. Measurements were made at room temperature between 15 and 25000 cm–1. The measured R(v) have a maximum below 100 cm–1 and then decrease for v 0. This low frequency behaviour of R(v) can be accounted for by considering a relevant extra-Drude contribution to the far infrared optical conductivity of YBCO. 相似文献