Low-temperature charge ordering in Sr₁₄Cu₂₄O₄₁

Synchrotron x-ray measurements were made between 20–300 K on single crystals of Sr₁₄Cu₂₄O₄₁, which has a quasi-one-dimensional chain and ladder structure, in order to investigate possible charge-ordering effects in the CuO₂ chains as indicated by recent NMR studies. At 50 K a few very weak satellite peaks were observed at (00l) positions corresponding to a fourfold increase in periodicity along the chain axis. These peaks decreased in intensity with increasing temperature, and eventually disappeared close to 300 K. The observations were interpreted in terms of a charge-ordered model involving both dimerization between two next-nearest-neighbor Cu²⁺ ions surrounding a Cu³⁺ ion on a Zhang-Rice singlet site, and dimerization between nearest-neighbor Cu²⁺ ions.