Investigation of Multiply Twins in Mn_2.02Co_0.98O₄ Ceramic by Means of Transmission Electron Microscopy

Abstract

Mn2.02Co0.98O4 ceramic with tetragonal spinel structure was prepared by solid‐state coordination reaction method. The phase and microstructure were studied using X‐ray diffractometer (XRD) and transmission electron microscope (TEM), respectively. The results show that the Mn2.02Co0.98O4 ceramic exhibits tetragonal spinel structure owing to imperfect quenching. Several kinds of defects were formed in the sample due to the phase transition from cubic spinel at high temperature to tetragonal spinel at room temperature. Two types of {112} twin wall were found in the quenched Mn2.02Co0.98O4 ceramic. The presence and the characteristics of twins were investigated. The twins arranged in a cyclic triangle form and the twin boundaries were parallel to (112) plane or (1¯12) plane. The possible mechanism for twinning arrangement in the triangle form was proposed according to some crystal geometry model analysis.

Enhanced conductivity and stability of Co 0.98Cu x Mn 2.02− x O 4 ceramics with dual phases and twin structures

“…It is reported that Co 0.98 Mn 2.02 O 4 can exist with a tetragonal spinel structure at room temperature, with a cubic spinel structure at high temperatures (T > 900 ℃) [10]. The cubic-to-tetragonal structural transition leads to the formation of twins [39][40][41]. However, the low carrier concentration in Co 0.98 Mn 2.02 O 4 results in high resistivity [10,41], which limits its applications to the fields involving low-temperature measurements and suppression of inrush current.…”