Evidence for $M_B$ and $M_C$ phases in the morphotropic phase boundary region of $(1-x)[Pb(Mg_{1/3}Nb_{2/3})O_3]-xPbTiO_3$ : A Rietveld study

TL;DR

This study identifies two distinct monoclinic phases within the morphotropic phase boundary of PMN-xPT using Rietveld analysis, revealing detailed phase boundaries and structures in this ferroelectric system.

Contribution

It provides experimental evidence for the coexistence of $M_B$ and $M_C$ monoclinic phases in the MPB region of PMN-xPT, refining the understanding of its phase diagram.

Findings

Identification of $M_B$ and $M_C$ monoclinic phases in specific composition ranges.

Confirmation of rhombohedral and tetragonal phases outside the MPB region.

Comparison of experimental results with Vanderbilt & Cohen's theoretical predictions.

Abstract

We present here the results of the room temperature dielectric constant measurements and Rietveld analysis of the powder x-ray diffraction data on $(1-x)[Pb(Mg_{1/3}Nb_{2/3})O_3]-xPbTiO_3$(PMN-$x$PT) in the composition range $0.20 \leq x \leq 0.45$ to show that the morphotropic phase boundary (MPB) region contains two monoclinic phases with space groups Cm (or $M_B$ type) and Pm (or $M_C$ type) stable in the composition ranges $0.27 \leq x \leq 0.30$ and $0.31 \leq x \leq 0.34$, respectively. The structure of PMN-$x$PT in the composition ranges $0 \leq x \leq$ 0.26, and $0.35 \leq x \leq1$ is found to be rhombohedral (R3m) and tetragonal (P4mm), respectively. These results are compared with the predictions of Vanderbilt & Cohen's theory.