The influence of Ti-doping on structural and multiferroic properties of yttrium manganite ceramics

Abstract

Hexagonal (P63cm) yttrium manganite, YMnO3, is a multiferroic material with ferroelectric transition at TC ≈ 900 K and antiferromagnetic transition at TN ≈ 70 K. Multiferroic behavior attracts a lot of attention because of its potential for various applications. The application possibilities are limited by large microcracking and microporosity of YMnO3 ceramics. In this work, the influence of Ti-doping on structural, ferroelectric and magnetic properties of YMnO3 ceramics was investigated. YMn1–xTixO3+δ (x = 0, 0.04, 0.08, 0.10, 0.15, 0.20) powders were prepared using sol-gel, polymerization complex method from citrate precursors, which were then calcinated at 900 °C for 4 h. The ceramic samples were obtained after sintering for 2 h at: 1400 °C for YMnO3, YMn0.96Ti0.04O3+δ, YMn0.92Ti0.08O3+δ and YMn0.90Ti0.10O3+δ; 1450 C for YMn0.85Ti0.15O3+δ; 1470 °C for YMn0.80Ti0.20O3+δ. X-ray diffraction (XRD), transmission and scanning electron microscopy (TEM and SEM) were used for structural and microstructural analysis of samples. Ferroelectric measurements of P(E) loops and leakage currents, and magnetic measurements of zero field cooled (ZFC) and field cooled (FC) M(T) curves, as well as M(H) curves, were enabled multiferroic characterization of ceramic samples. The samples x = 0 and 0.04 are crystallized in a single phased hexagonal structure, (P63cm), the samples x = 0.08 and 0.10 exhibited the presence of both hexagonal phase and rhombohedral phase (R3c), and the samples x = 0.15 and 0.20 are crystallized in rhombohedral 1×1×3 superstructure. Ti-doped YMnO3 ceramic samples showed reduced density of microcracks, and inter- and intragranular pores, and large increase in relative density (greater than 90 %) for YMn1–xTixO3+δ (x = 0.10, 0.15 and 0.20) samples. Leakage currents for most of doped samples were lower than leakage current of undoped sample, but the ferroelectric response was not significantly improved. Doping of YMnO3 with nonmagnetic Ti4+ led to suppression of antiferromagnetic ordering visible through decrease of the Néel temperature and Weiss parameter and the appearance of weak ferromagnetism.