Structural trends from a consistent set of single-crystal data of REFeAsO (RE = La, Ce, Pr, Nd, Sm, Gd, and Tb)

Abstract

A new crystal growth technique for single-crystals of REFeAsO (RE = La, Ce, Pr, Nd, Sm, Gd, and Tb) using NaI/KI as flux is presented. Crystals with a size up to 300 $μ$m were isolated for single-crystal X-ray diffraction measurements. Lattice parameters were determined by LeBail fits of X-ray powder data against LaB6 standard. A consistent set of structural data is obtained and interpreted in a hard-sphere model. Effective radii for the rare-earth metal atoms for REFeAsO are deduced. The relation of the intra- and inter-plane distances of the arsenic atoms is identified as limiter of the phase formation, and its influence on Tc is discussed.

8 pages, 11 figures, 3 tables, fig. 6 changed to numerical plot, minor changes to the text, accepted for publication in PRB