A new family of ferroelectric tetragonal tungsten bronze phases, Ba2MTi2X3O15

Towards novel multiferroic and magnetoelectric materials: dipole stability in tetragonal tungsten bronzes

“…Similar behaviour has been seen in the ferroelectric TTB series Ba 2 RE 4 Ti 2 Nb 8 O 30 RE = La, Pr, Nd, Sm, Eu, Gd and Dy) [32,[34][35][36][37] where with decreasing size there is a cross over from relaxor to ferroelectric behaviour and T C is increasingly stabilized. Chen and co-workers [38] have suggested that it is not the average size of the A-cation which is important for ferroelectric ordering, but rather the difference in size of the A-cation species, which appears to be supported by our results where the dipole stability scales not with average size but with the degree of size mismatch (variance).…”

Growth and Characterization of Centimeter‐Sized Ba2LaFeNb4O15 Crystals from High‐Temperature Solution under a Controlled Atmosphere

“…In Ba 2 RENb 3 Ti 2 O 15 compounds, deviations from the ideal TTB symmetry caused by an incommensurate modulation was associated with relaxor behavior, whereas a commensurate modulation was observed for phases exhibiting ferroelectric behavior. [56][57][58][59][60] The above examples demonstrate the intricate relationships between the composition, structure, and properties of TTB systems, which were illustrated in an original way by the study of Ba 2 REFeNb 4 O 15 composite multiferroic ceramics. [61] At room temperature, the crystal structure of Ba 2 REFeNb 4 O 15 was described in a "pseudotetragonal" symmetry, space group Pba2 (no.…”

Microstructural and high-temperature impedance spectroscopy study of Ba6MNb9O30 (M=Ga, Sc, In) relaxor dielectric ceramics with tetragonal tungsten bronze structure

“…The A1 sites are 12-coordinated and defined by 8 octahedra, the four larger A2 sites are 15-coordinated and defined by 10 octahedra, while the four trigonal C-sites are 9-coordinated and defined by 6 octahedra; moreover, the BO 6 octahedra are non-equivalent (two B1 sites and eight B2 sites) - Figure 1. This rich diversity of elements which can be incorporated into the TTB structure allows for compositional tuning that has been exploited for development of new phases [13,19] ranging from ferroelectrics [20][21][22] to microwave dielectrics [23,24] and to ionic conductors [25]. During the last few years, the research dedicated to novel TTB ferroelectric and ferroelectric-related materials resurrected [15][16][17][18][19][20][21][22][26][27][28][29][30][31], with the Ba 6 FeNb 9 O 30 (BFNO) [32][33][34][35] as starting point.…”

“…This rich diversity of elements which can be incorporated into the TTB structure allows for compositional tuning that has been exploited for development of new phases [13,19] ranging from ferroelectrics [20][21][22] to microwave dielectrics [23,24] and to ionic conductors [25]. During the last few years, the research dedicated to novel TTB ferroelectric and ferroelectric-related materials resurrected [15][16][17][18][19][20][21][22][26][27][28][29][30][31], with the Ba 6 FeNb 9 O 30 (BFNO) [32][33][34][35] as starting point. Earlier data reported that BFNO is ferroelectric with T C values either in the range 133-138 K [36] or 570-583 K [37,38], however being not electrically homogeneous [29] and with oxygen vacancy gradients due to the variable oxidation state of Fe (Fe 3+ /Fe 2+ ); both low temperature dielectric spectroscopy and high temperature impedance spectroscopy measurements indicated more electroactive regions than anticipated [16].…”