TY - JOUR
T1 - Tungsten Bronze Barium Neodymium Titanate (Ba6-3nNd8+2nTi18O54)
T2 - An Intrinsic Nanostructured Material and Its Defect Distribution
AU - Azough, Feridoon
AU - Cernik, Robert Joseph
AU - Schaffer, Bernhard
AU - Kepaptsoglou, Demie
AU - Ramasse, Quentin Mathieu
AU - Bigatti, Marco
AU - Ali, Amir
AU - MacLaren, Ian
AU - Barthel, Juri
AU - Molinari, Marco
AU - Baran, Jakub Dominik
AU - Parker, Stephen Charles
AU - Freer, Robert
N1 - No record of this in Eprints. No accepted date. HN 07/11/2017
PY - 2016/4/18
Y1 - 2016/4/18
N2 - We investigated the structure of the tungsten bronze barium neodymium titanates Ba6-3nNd8+2nTi18O54, which are exploited as microwave dielectric ceramics. They form a complex nanostructure, which resembles a nanofilm with stacking layers of ∼12 Å thickness. The synthesized samples of Ba6-3nNd8+2nTi18O54 (n = 0, 0.3, 0.4, 0.5) are characterized by pentagonal and tetragonal columns, where the A cations are distributed in three symmetrically inequivalent sites. Synchrotron X-ray diffraction and electron energy loss spectroscopy allowed for quantitative analysis of the site occupancy, which determines the defect distribution. This is corroborated by density functional theory calculations. Pentagonal columns are dominated by Ba, and tetragonal columns are dominated by Nd, although specific Nd sites exhibit significant concentrations of Ba. The data indicated significant elongation of the Ba columns in the pentagonal positions and of the Nd columns in tetragonal positions involving a zigzag arrangement of atoms along the b lattice direction. We found that the preferred Ba substitution occurs at Nd[3]/[4] followed by Nd[2] and Nd[1]/[5] sites, which is significantly different to that proposed in earlier studies. Our results on the Ba6-3nNd8+2nTi18O54 "perovskite" superstructure and its defect distribution are particularly valuable in those applications where the optimization of material properties of oxides is imperative; these include not only microwave ceramics but also thermoelectric materials, where the nanostructure and the distribution of the dopants will reduce the thermal conductivity.
AB - We investigated the structure of the tungsten bronze barium neodymium titanates Ba6-3nNd8+2nTi18O54, which are exploited as microwave dielectric ceramics. They form a complex nanostructure, which resembles a nanofilm with stacking layers of ∼12 Å thickness. The synthesized samples of Ba6-3nNd8+2nTi18O54 (n = 0, 0.3, 0.4, 0.5) are characterized by pentagonal and tetragonal columns, where the A cations are distributed in three symmetrically inequivalent sites. Synchrotron X-ray diffraction and electron energy loss spectroscopy allowed for quantitative analysis of the site occupancy, which determines the defect distribution. This is corroborated by density functional theory calculations. Pentagonal columns are dominated by Ba, and tetragonal columns are dominated by Nd, although specific Nd sites exhibit significant concentrations of Ba. The data indicated significant elongation of the Ba columns in the pentagonal positions and of the Nd columns in tetragonal positions involving a zigzag arrangement of atoms along the b lattice direction. We found that the preferred Ba substitution occurs at Nd[3]/[4] followed by Nd[2] and Nd[1]/[5] sites, which is significantly different to that proposed in earlier studies. Our results on the Ba6-3nNd8+2nTi18O54 "perovskite" superstructure and its defect distribution are particularly valuable in those applications where the optimization of material properties of oxides is imperative; these include not only microwave ceramics but also thermoelectric materials, where the nanostructure and the distribution of the dopants will reduce the thermal conductivity.
UR - http://www.scopus.com/inward/record.url?scp=84963984182&partnerID=8YFLogxK
U2 - 10.1021/acs.inorgchem.5b02594
DO - 10.1021/acs.inorgchem.5b02594
M3 - Article
AN - SCOPUS:84963984182
VL - 55
SP - 3338
EP - 3350
JO - Inorganic Chemistry
JF - Inorganic Chemistry
SN - 0020-1669
IS - 7
ER -