New Mechanism for Ferroelectricity in the Perovskite Ca_2–xMn_xTi₂O₆ Synthesized by Spark Plasma Sintering

Abstract

Perovskite oxides hosting ferroelectricity are particularly important materials for modern technologies. The ferroelectric transition in the well-known oxides BaTiO and PbTiO is realized by softening of a vibration mode in the cubic perovskite structure. For most perovskite oxides, octahedral-site tilting systems are developed to accommodate the bonding mismatch due to a geometric tolerance factor t = (A-O)/[√2(B-O)] < 1. In the absence of cations having lone-pair electrons, e.g., Bi and Pb, all simple and complex A-site and B-site ordered perovskite oxides with a t < 1 show a variety of tilting systems, and none of them become ferroelectric. The ferroelectric CaMnTiO oxide is, up to now, the only one that breaks this rule. It exhibits a columnar A-site ordering with a pronounced octahedral-site tilting and yet becomes ferroelectric at T ≈ 650 K. Most importantly, the ferroelectricity at T < T is caused by an order-disorder transition instead of a displacive transition; this character may be useful to overcome the critical thickness problem experienced in all proper ferroelectrics. Application of this new ferroelectric material can greatly simplify the structure of microelectronic devices. However, CaMnTiO is a high-pressure phase obtained at 7 GPa and 1200 °C, which limits its application. Here we report a new method to synthesize a gram-level sample of ferroelectric CaMnTiO, having the same crystal structure as CaMnTiO and a similarly high Curie temperature. The new finding paves the way for the mass production of this important ferroelectric oxide. We have used neutron powder diffraction to identify the origin of the peculiar ferroelectric transition in this double perovskite and to reveal the interplay between magnetic ordering and the ferroelectric displacement at low temperatures.

Spin freezing into a disordered state in CaFeTi2O6 synthesized under high pressure

“…In contrast to CFTO, Mn 2+ at the coplanar site in CMTO stays off the plane. It is the order-disorder transition of this displacement that induces a ferroelectric transition at T c [4]. A type-C magnetic ordering occurs at T N ≈ 8 K. The difference of orbital occupation between Fe 2+ and Mn 2+ and/or the displacement at the coplanar site of MnO 4 may contribute to the absence of magnetic ordering in CFTO.…”

“…Double perovskites with the general formula AA'BB'O 6 can accommodate a variety of cation ordering at both A and B sites [1], which host complex orbital/spin orderings, colossal magnetoresistance [2], charge transfer and disproportionation [3], and multiferroic properties [4,5]. There are a total of 15 tilting systems to describe the cornersharing BO 6 octahedral tilting in the subgroups as the symmetry lowers from the cubic structure (Pm-3m) of simple perovskite ABO 3 [6].…”

Half-Metallic Property Induced by Double Exchange Interaction in the Double Perovskite Bi2BB′O6 (B, B′ = 3d Transitional Metal) via First-Principles Calculations

“…In the search for new half-metallic materials, the double perovskite structure is a suitable template due to its flexibility and ease of illustrating an abundance of material properties, such as band insulators, ferromagnets, and ferroelectrics [3,16,17,18]. Organic double perovskites have recently been utilized for their remarkable optoelectronic properties [19,20,21,22,23,24,25].…”

First‐principles Studies of Band Gap Engineering in Ferroelectric Oxides

“…Comparison of the experimental and DFT‐relaxed structures showed that a decrease of 0.14 Å in the distance of the planar Mn−O bond leads to the band gap change of 1.2 eV between the two structures. The shorter planar Mn−O distances in the DFT‐relaxed structure is due to the tendency of DFT to overestimation the TiO 6 octahedral rotation angles that has been previously observed in other ferroelectric perovskites . However, Gou et al .…”