Physical Review B (Impact Factor: 3.74). 11/1987; 36(16):8320-8324. DOI: 10.1103/PhysRevB.36.8320
We have studied the Cu-O vibrations in the MBa2Cu3O7 systems with M=Y,Eu,andGd by Raman spectroscopy. The observed Raman features are similar in the three systems. The four Raman bands in the 300-700 cm-1 frequency region exhibit isotopic shifts upon O18 substitution implying that these modes involve oxygen vibrations. In oxygen-deficient YBa2Cu3O7- samples prepared in the range 0< <0.7 within the orthorhombic structure, the A1g axial stretch mode is found to undergo both a softening and broadening with increasing oxygen deficiency. Furthermore, the Raman feature in the 550-600 cm-1 region shows an increase in intensity. The latter is attributed to disorder activation of the Cu-O chain mode, normally forbidden in the stoichiometric compound. These features and the emergence of a distinct Raman peak near 390 cm-1 in oxygen-deficient samples suggest that Raman spectroscopy could be used for characterizing oxygen stoichiometry of high-Tc superconductors.
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[Show abstract][Hide abstract] ABSTRACT: Insulator–conductor composites are touted as excellent materials for charge storage capacitor applications. Cupric oxide (CuO) decked few-layered graphene (FLG) can be one such composite. Understanding the dielectric behaviour of CuO–graphene system, which is anticipated to be intricate, is definitely an attention-grabbing one. Here, CuO decked FLG composite is synthesized using molecular level mixing. Samples with different amounts of FLG (low and high amount FLG containing samples are named as CuO-0.1G and CuO-0.2G, respectively) are prepared. At 1 kHz, dielectric permittivity (ε1) values of CuO-0.1G (ε1 = 318) and CuO-0.2G (ε1 = 667) are ∼1.1 and ∼2.3 times greater, respectively than that of CuO (ε1 = 289). Increase in ε1 is ascribed to the formation of continuous conductive pathway between CuO decked FLG sheets. AC conductivity (σ) of CuO-0.1G and CuO-0.2G samples is found to increase with applied frequency and follows Jonscher’s power law. Experimental data pertaining to AC conductivity could be easily fitted to quantum mechanical tunnelling model. The fitting results suggest electron hopping mechanism as the cause for enhanced AC conductivity. This work gives a great motivation to develop composite materials (with conducting and insulating constituents) whose dielectric behaviour can be controlled by mechanisms occurring at atomistic scale.
[Show abstract][Hide abstract] ABSTRACT: Single crystals of superconducting BaâMCuâO/sub x/ (M = Y, Gd) have been used for a study of the polarization dependence of the Raman spectra so as to better understand the lattice dynamics and the role of O defects in these materials. Several prominent vibrational bands have strong polarization dependence and can all be attributed to specific modes with A/sub g/ symmetry. Broad features between 500 and 600 cmâ»Â¹ are suggested to be related to O vacancy disorder.
[Show abstract][Hide abstract] ABSTRACT: Raman scattering data from superconducting phases of SmBa2Cu3Ox subject to different heat treatments are reported and compared with those of the impurity phase BaCuO2. It is found that the high frequency 640 cm-1 mode corresponds to a characteristic vibration within the superconducting phase. Its sensitivity to heat treatment conditions and to oxygen content suggest an assignment of the mode to the Cu(1)-O(1) stretching vibration.
Physica C Superconductivity 10/1988; 156(3):420-426. DOI:10.1016/0921-4534(88)90766-6 · 0.94 Impact Factor