Antiferromagnetism in YBa2Cu3O6+x: Ga and Zn substitutions I. 89Y NMR determination of the Néel temperature

The Néel temperature TN of YBa2(Cu1-yMy)3O6+x for pure (0<x<0.3) and M = Zn and Ga doped samples (x<0.2) has been measured from the abrupt increase of the 89Y NMR width with decreasing T. A rather weak variation of TN and of the NMR width in the antiferromagnetic state has been detected upon Zn or Ga doping. This leads us to conclude that a majority of Zn atoms are substituted on the Cu (1) site. In the absence of paramagnetic moments on the Cu (1) layer, the magnetic interactions between CuO2 bilayers might be assigned to dipole-dipole couplings, except if the correlation length for the 2D bilayers has a much steeper T dependence than for La2CuO4. A detailed analysis of the hole doping in the pure compounds is attempted. © 1990.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Conductivity and electron density of undoped model compounds of poly(phenylene vinylene)

Fourteen derivatives of trans,trans-1,4-bis[2-phenylethenyl]benzene were synthesized by Wittig reactions as model compounds of poly(paraphenylene vinylene). Structure, configurational homogeneity and absence of ionic impurities were controlled by mass spectrometry, infrared and neutron activation analysis, respectively. Crystallographic unit cell parameters were obtained from X-ray powder patterns and measurements of electrical conductivities were performed on undoped samples. The data of four more compounds containing one or more thiophene rings instead of phenyl rings were added from the 3iterature. If NO2 and Cl groups are excluded from the electron count a good linear correlation is found between the logarithm of the conductivity and the non-σ electron density (e A ̊-3). The position of the substituents, on the central or on the terminal ring, also plays a role in as much as it affects the molecular volume of the compound but not the non-σ electron density. The correlation between the logarithm of the conductivity and the absorption coefficient of the longest wavelength of UV absorption identifies the π electrons in the chromophore as the principal charge carriers. © 1990.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Effect of zinc and iron on the (micro-)structure and copper charge excess of the YBaCuO superconductor

SCOPUS: ar.jinfo:eu-repo/semantics/publishe