New pyrochlore-type oxides in Ca–R–Ti–Nb–O system (R=Y, Sm or Gd)—structure, FT-IR spectra and dielectric properties

Crystal structural and optical properties of Cr-doped Y2Ti2O7 and Y2Sn2O7 pyrochlores

“…This is very close to the limit also found in REE-stannates on decreasing cell parameter caused by decreasing REE ionic radii (see Figures 3 and 4 in [12]). The occurrence of a lower limit (about 204 pm) on the <B-O> distance in Y-stannates upon substitutions in the A or B sub-networks can be interpreted considering that in the PS0 sample (pure Sn-term) all the Sn-O distances are already much shorter than the sum of the ionic radii of [4] O 2-(138 pm) and [6] Sn 4+ (69 pm) [35]. This means that the SnO6 octahedron experiences a quite strong compression, which is further increased by incorporation of Cr into it.…”

“…Compounds exhibiting the pyrochlore structure have been extensively investigated, especially for their properties of anion and mixed conduction [1,2], magneto-resistance [3] and superconductivity [4] due to their ability to incorporate an incredibly wide range of elements. A great deal of applications have been envisaged, including sensors and transistors [5], dielectrics and fast ion conductors [1,6], electrocatalysts [7] or actinide host phase for nuclear waste encapsulation [8]. In particular, titanate and stannate pyrochlores have been synthesised since forty years [9][10][11], so that a deep knowledge of their structural trends [12], thermodynamic properties [13], disorder [14,15] and nonstoichiometry [16] has been developed.…”

New Family of Dielectric Materials in Ca–Y–Ti–Nb–O System Having Pyrochlore Type Structure

“…Apparently, even when the number of different metal ions is varied in an arbitrary manner, if the M to O ratio is maintained 4:7, the resultant compound has a pyrochloretype structure. (Earlier we had prepared Ca 3 RE 3 Ti 7 Nb 2 O 26.5 [RE 5 rare earth], 13 in which there were a large number of Ti ions in the compound compared with other metals, and still had a pyrochlore-type structure). Moreover, in the present series, there was also a wide variation in the number of metal atoms, but the pyrochlore structure was retained.…”

Preparation, Characterization, Photocatalytic Activity and Conductivity Studies of YLnTi2O7(Ln = Nd, Sm, Eu and Gd)

“…These oxides possess high oxygen ion conductivity, 2, 3 excellent microwave dielectric characteristics, 4 optical nonlinearity, 5 high radiation tolerance, 6 magneto-resistance, superconductivity, 7,8 high chemical stability, high refractive index and good catalytic activity. [9][10][11][12] They are used as sensors, transistors, 9 thermal barrier coatings, 13,14 fast ion conductors, 1,15 high permittivity dielectrics, 14 electrocatalysts 16 and for nuclear waste encapsulation. 17 The structure of pyrochlore is characterized by corner sharing of BO 6 octahedra forming a B 2 O 6 network which intersects with A-O chains of formula A 2 O.…”