New phase of BaLaMnO_4-x formed by annealing in a reducing atmosphere

Abstract

A single crystal of BaLaMnO₄ with I4/mmm has been synthesized by a floating zone method. A new phase of BaLaMnO_4-x was obtained by annealing the single crystal in a reducing atmosphere at 773 K for 168 h. The structural change was analyzed by four-circle X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The new phase has an orthorhombic unit cell (Cccm) of a=0.5504(7) nm, b=0.5502(5) nm, and c=1.3265(1) nm. The structural change from I4/mmm into Cccm was caused by an oxygen deficiency, and a small amount of Mn²⁺ ions was formed by annealing in a reducing atmosphere.