Effect of rotation of feed and seed rods on the quality of Na0.75CoO2 single crystal grown by traveling solvent floating zone method

TL;DR

This study investigates how the rotation of feed and seed rods affects the growth quality of Na0.75CoO2 single crystals using the floating zone method, revealing critical factors for high-quality crystal production.

Contribution

It demonstrates the importance of rod rotation in crystal growth and explores phase separation and impurity formation under different conditions.

Findings

Rotation influences crystal quality and phase purity.

Phase separation into Na-rich and Na-poor domains occurs during growth.

Magnetic transitions observed at 22 K and around 334-339 K.

Abstract

High purity Na0.75CoO2 single crystals have been grown by floating zone method. We found the rotation of feed and seed rods play a crucial role in growing high quality single crystal. Systematic investigations suggest the occurrence of a phase separation at microscopic level, such as the separation into Na-rich and Na-poor domains during the growth, and formation of impurity phase(s) depending on growth conditions. NaxCoO2 (x = 0.30, 0.60) crystals have been prepared by sodium deintercalation from Na0.75CoO2. Powder X-ray and energy dispersive X-ray analyses have confirmed the phase purity and homogeneity of the samples. Magnetic susceptibility measurements of x = 0.60 and 0.75 crystals indicate a bulk phase transition at 22 K and an anomaly around 339 K and 334 K respectively which are attributed to structural transition. In addition some unique features related to Na0.60CoO2 were observed.