Correlations of structural, magnetic, and dielectric properties of undoped and doped CaCu3Ti4O12

TL;DR

This study investigates how doping and processing affect the structural, magnetic, and dielectric properties of CaCu3Ti4O12 ceramics, revealing significant changes in dielectric behavior and magnetic correlations due to low-level doping.

Contribution

It provides a detailed analysis of doped and undoped CCTO ceramics, highlighting the impact of low-level doping on dielectric and magnetic properties and exploring potential magnetoelectric coupling effects.

Findings

Doping with Mn or Fe drastically reduces dielectric constant and conductivity.

Ni doping causes only slight changes in dielectric properties.

Doping and tempering significantly influence the Curie-Weiss constant and magnetic behavior.

Abstract

The present work reports synthesis, as well as a detailed and careful characterization of structural, magnetic, and dielectric properties of differently tempered undoped and doped CaCu3Ti4O12 (CCTO) ceramics. For this purpose, neutron and x-ray powder diffraction, SQUID measurements, and dielectric spectroscopy have been performed. Mn-, Fe-, and Ni-doped CCTO ceramics were investigated in great detail to document the influence of low-level doping with 3d metals on the antiferromagnetic structure and dielectric properties. In the light of possible magnetoelectric coupling in these doped ceramics, the dielectric measurements were also carried out in external magnetic fields up to 7 T, showing a minor but significant dependence of the dielectric constant on the applied magnetic field. Undoped CCTO is well-known for its colossal dielectric constant in a broad frequency and temperature range. With the present extended characterization of doped as well as undoped CCTO, we want to address the question why doping with only 1% Mn or 0.5% Fe decreases the room-temperature dielectric constant of CCTO by a factor of ~100 with a concomitant reduction of the conductivity, whereas 0.5% Ni doping changes the dielectric properties only slightly. In addition, diffraction experiments and magnetic investigations were undertaken to check for possible correlations of the magnitude of the colossal dielectric constants with structural details or with magnetic properties like the magnetic ordering, the Curie-Weiss temperatures, or the paramagnetic moment. It is revealed, that while the magnetic ordering temperature and the effective moment of all investigated CCTO ceramics are rather similar, there is a dramatic influence of doping and tempering time on the Curie-Weiss constant.