Several Niobium oxides of formula Ba2LnFeNb4O15 (Ln = La, Pr, Nd, Sm, Eu, Gd) with the Tetragonal Tungsten Bronze (TTB) structure have been synthesised by conventional solid-state methods. The Neodymium, Samarium and Europium compounds are ferroelectric with Curie temperature ranging from 320 to 440K. The Praseodymium and Gadolinium compounds behave as relaxors below 170 and 300 K respectively. The Praseodymium, Neodymium, Samarium, Europium and Gadolinium compounds exhibit magnetic hysteresis loops at room temperature originating from traces of a barium ferrite secondary phase. The presence of both ferroelectric and magnetic hysteresis loops at room temperature allows considering these materials as composites multiferroic. Based on crystal-chemical analysis we propose some relationships between the introduction of Ln3+ ions in the TTB framework and the chemical, structural and physical properties of these materials.
@article{arxiv.0707.3112,
title = {The Ba2LnFeNb4O15 Tetragonal Tungsten Bronze: towards RT composite multiferroics},
author = {M. Josse and O. Bidault and F. Roulland and E. Castel and A. Simon and D. Michau and R. Von der Muhll and O. Nguyen and M. Maglione},
journal= {arXiv preprint arXiv:0707.3112},
year = {2008}
}
Comments
Revised version after identification of a spurious barium ferrite phase responsible for composite multiferroic properties at RT. Appearance of this parasitic phase is correlated to the crystal-chemistry of the Ba2LnFeNb4O15 TTBs. Submitted to Solid State Sciences. 27 pages, 7 figures, 3 tables