Investigation of the Defect Structure of Congruent and Fe-Doped LiNbO₃ Powders Synthesized by the Combustion Method.

You-Yun Li,Guo-Ju Chen,Weng-Sing Hwang,Chia-Liang Kuo,Hao-Long Chen,Ping-Hung Hsieh

doi:10.3390/ma10040380

You-Yun Li, Guo-Ju Chen + Show 4 more

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https://doi.org/10.3390/ma10040380

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Abstract

Fe-doped LiNbO3 synthesized by the combustion method to seek new multiferroic materials exhibits room-temperature ferromagnetism, as reported in our previous work. In this work, the defect structure of congruent and Fe-doped LiNbO3 (0.57–3.3 mol %) powders was investigated in detail by several methods. The molar ratio of [Li]/([Li]+[Nb]) was determined by the Curie temperature (Tc) via DSC. Two peaks of Tc were observed due to phase splitting, and the phase at lower Tc disappears as the Fe doping concentration increases. The coexistence of two different oxidation states of Fe ions in LiNbO3 was probed by XPS and UV-Vis spectroscopy. The Raman spectra exhibit displacements along the c axis of Li and Nb ions, and a deformation of the NbO6 framework owing to Fe doping. Several doping models were applied in the Rietveld refinement of powder X-ray diffraction collected by synchrotron radiation. The fitting by the Nb vacancy model leads to an improbably distorted structure of congruent LiNbO3. In Fe-doped LiNbO3, we conjecture that Li and Nb vacancies coexist in the lattice structure; Fe+2/Fe+3 ions are substituted for Li ions at the regular Li site and may push the anti-site NbLi ion back to the regular Nb site.

Highlights

The discovery of the single-phase multiferroic materials with high magnetoelectric susceptibility in room temperature for the intention of advanced functional devices fabrication and the investigation of the mechanism of the magnetoelectric coupling phenomena have been so far essential in the field of research [1,2,3]
Several intrinsic defect models have been proposed in the literature to describe congruent LiNbO3
Two Tc peaks were observed in differential scanning calorimetry (DSC) due to phase splitting [36], and the phase at lower Tc disappears with an increase in doping Fe concentration, which reveals that congruent LiNbO3 and

Summary

Introduction

The discovery of the single-phase multiferroic materials with high magnetoelectric susceptibility in room temperature for the intention of advanced functional devices fabrication and the investigation of the mechanism of the magnetoelectric coupling phenomena have been so far essential in the field of research [1,2,3]. One is materials with magnetic ordering-induced multiferroic behavior, in which electric polarization is induced in a magnetically ordered state like complex spin structures, but a major limitation to further use is the low phase transformation temperature. The other type is the perovskite-type compound, in which the electric polarization and the magnetic coupling are donated by different ions in the lattice structure, and the Curie temperature is high enough for devices working at room temperature but the magnetoelectric coupling is small.

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