T*-type substituted neodymium cuprates Nd 1.2Sr 0.8− xY(Ho, Er, Yb) xCuO 4− δ: crystal chemistry and electrical conductivity

Abstract

The four T*-type solid solutions Nd 1.2Sr 0.8− x RE x CuO 4− δ (RE=Y, Ho, Er, Yb) were synthesized and studied in terms of homogeneity range, structural study (neutron powder diffraction) and electrical conductivity. The homogeneity ranges have a small extent around the value x=0.4. The main crystal chemical properties are as follows: a full ordering of Sr 2+ and Y 3+ (Ho, Er, Yb) in the Rocksalt (RS) and Calcium Fluoride (CF) slabs, respectively, Nd 3+ distributed on both slabs; an overall oxygen deficiency δ in the range 0.15–0.18; oxygen vacancies distributed in the CF slabs (12%) and the equatorial “CuO 2” planes; interstitial oxygen in the RS slabs (# Nd 0.6Sr 0.4O 1.04). Electrical resistivity measurements (RT — 4 K) of samples annealed under p O 2 up to 1800 bars point to a “dirty metal” behavior up to 25 K (Y, Ho) and 70 K (Er), followed by a semiconductive regime at lower temperature. The big difficulty to get a superconductive transition in these phases and more generally in the T*-type cuprates is strongly dependent on the nature and the amount of small lanthanoı̈dic cation in the CF slabs.