Ferroelectricity in Perovskites with s⁰ A‐Site Cations: Toward Near‐Room‐Temperature Multiferroics

Abstract

Magnetic ferroelectric (FE) materials (that is, multiferroics) have received much attention and can have wide technological applications owing to the possibility of controlling their electric properties and their magnetic properties by electric fields. [1, 2] An important class of multiferroic and FE [3] materials is based on perovskites, ABO anion). In most cases, the A cations are small, so that t < 1 and the AÀO bonds are too long to maintain the ideal cubic structure. Consequently, the A cation moves away from the center of the B 8 cube, which is accompanied by the bending of the B-O-B bonds and the rotation of the BO 6 octahedra to form a lower-coordinate AO n polyhedron (n < 12) with short AÀO bonds. The distortion of the ideal cubic perovskite toward a non-centrosymmetric FE structure requires another local instability apart from t < 1, namely, the second-order Jahn-Teller (SOJT) instability [4][5][6] of the A-site and/or B-site cation.As found for PbTiO 3 , [7] PbVO 3 , [8] and BiCoO 3 , [9] moving the A cation toward the center of one B 4 face (Figure 1 a) leads to a tetragonal FE structure with space group P4mm. The B cations move away from the approaching A cations such that the coordinate environment of each B cation is more like a BO 5 square pyramid with shortened axial B À O bond. In PbTiO 3 , PbVO 3 , and BiCoO 3 , the s 2 A-site cations Pb 2+ and Bi 3+ are susceptible to a SOJT distortion, which mixes the empty 6p orbital of A into the filled 6s 2 orbital of A hence forming a lone pair on A.[4] In PbTiO 3 , the B-site cation Ti 4+ (d 0 ) is also susceptible to a SOJT distortion, which mixes the empty Ti 3d orbitals into the filled 2p orbitals of the oxygen atom of the axial Ti À O bond. [5,6] Thus, in PbTiO 3 , the need to make short PbÀO bonds and the SOJT instabilities of both Pb 2+ and Ti 4+ ions cooperate to give rise to the observed FE distortion. [10, 11] Another type of the A-cation displacement from the center of the B 8 cube is the movement toward one corner of the B 8 cube along the body-diagonal direction (that is, the C 3 rotational axis; Figure 1 b) to form a non-centrosymmetric FE trigonal structure with space group R3c, as found for BiFeO 3 .[12] The movement of the A cation toward one corner is equivalent to that toward the opposite corner, and the two energetically-equivalent FE structures are mutually interconverted through the centrosymmetric paraelectric (PE) trigonal structure with space group R3 c (Figure 1 c). [13, 14] For BiFeO 3 , the FE Curie temperature (T E = 1123 K) [15] and the three-dimensional antiferromagnetic ordering temperature (T N = 650 K) [16] are well above room temperature. For with space group R3c. For simplicity, only the two BO 6 octahedra at the two corners of the B 8 cube along the body-diagonal direction and the AO 3 unit lying between the two octahedra are shown. The AO 3 unit merges with the upper BO 6 octahedron to form a distorted AO 6 octahedron, which shares its face with the upper BO 6 octahedron, resulting in the face-sharing octahe...

(In1−yMny)MnO3 (1/9≤y≤1/3): Unusual Perovskites with Unusual Properties

“…[11][12][13] Herein, we report on the stabilization of new perovskite oxides (In 1Ày Mn y )MnO 3 (1/9 y 1/3) using a high-pressure high-temperature technique. Not only is the discovery of new simple ABO 3 perovskites extremely rare these days, but (In 1Ày Mn y )MnO 3 perovskites are very unusual in a few ways.…”

“…[ 12 (Z = 1), where A, B1, and B2 stand for the A site and two B sites of the perovskite structure. The structural analysis showed that all the oxygen sites are fully occupied.…”

Achieved High Energy Density and Excellent Thermal Stability in (1-x)(Bi0.5Na0.5)0.94Ba0.06TiO3-xBi(Mg0.5Ti0.5)O3&nbsp;Relaxor Ferroelectric Thin Films

“…In the first place, the ionic radius of Mg 2+ is larger than that of Ti 4+ , so the Bsite Mg 2+ substitution can increase the relative ionic displacement and thus improve the dipole polarizability [40]. In the second place，the substitution of Mg 2+ causes the distortion of TiO 6 octahedra, which conduces to the improvement of P max of Bi(Mg 0.5 Ti 0.5 )O 3 doped thin films [41]. What's more, the remnant polarization of the thin films increases slightly from 6.75 to 8.60 μC/cm 2 with the addition of BMT from 0.3 to 0.6.…”

Relaxation of ferroelectric thin films of diisopropylammonium perchlorate

“…[3][4][5][6][7] Presently, applications of ferroelectrics are dominated by inorganic perovskite-type materials, such as lead zirconate titanate (PZT) and barium titanate (BTO). [8][9][10][11] It should be noted that ferroelectricity was first discovered in an organic crystal, Rochelle salt, 12 and later some other molecular crystals were found to be ferroelectric, such as triglycine sulfate and thiourea. The mechanism of most molecular ferroelectrics comes from order-disorder transition, while that of inorganic perovskite ferroelectrics comes from displacement of cations and/or anions.…”