# Bond-valence analysis of the charge distribution and internal stresses in the $RBa_2Cu_30_{7-\delta}$ system (R =rare earth)

Ramesh, S and Hegde, MS (1994) Bond-valence analysis of the charge distribution and internal stresses in the $RBa_2Cu_30_{7-\delta}$ system (R =rare earth). In: Physica C: Superconductivity, 230 (1-2). pp. 135-140.

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## Abstract

The influence of rare-earth ions on the crystal chemistry, charge distribution and internal stresses in $RBa_2Cu_3O_{7-\delta}$ (R=rare- earth ion) system has been analyzed in terms of the bond-valence sums (BVS) using the structural data of Guillaume et al. [Z. Phys. B 90 (1993) 13 ]. The bond valences on both Cu ( 1 ) and Cu (2) sites increase with decreasing rare-earth ionic radius. The proportion of $Cu^{3+}$ varies from 14.6 to 38.9% at the Cu ( 1 ) site and from 11.3 to 31.1 % at the Cu (2) site for R varying from La to Yb. While the bond-valence sums on La, Pr, and Nd are significantly more than the nominal valence of 3 indicative of a larger ion in the lattice cage, other rare-earth ions with a valence less than 3, show evidence for a eompressional stress in the system. A valence sum of 3.39 on Pr suggests a supratrivalent Pr ion in $PrBa_2Cu_3O_{7-\delta}$. The compressional strain in the barium cage in- creases with decreasing rare-earth ionic radius, forcing an increasing orthorhombic distortion. The bond-valence sums on all the oxygens except 0(4) are around 2 and they show little variation with the rare-earth size. A relatively lower bond valence on 0(4) suggests that this oxygen is more likely to share the holes on copper.

Item Type: Journal Article The copyright of this article belongs to Elsevier. Division of Chemical Sciences > Solid State & Structural Chemistry Unit Anka Setty 30 Jun 2006 19 Sep 2010 04:29 http://eprints.iisc.ac.in/id/eprint/7752