Subsolidus phase equilibria and properties in the system Bi2O3:Mn2O3±x:Nb2O5

Phase Formation and Properties in the System Bi2O3:2CoO1+x:Nb2O5

“…The consistent observation of this reflection indicates that all Bi-Co-Nb-O pyrochlores exhibit positional displacements. Furthermore, the [29] Fe, [36] Mn [37] ), occurs at substantially lower Bi concentrations than conventional formulations placing only Bi on the A sites and the smaller M/Nb cations on the B sites. The pyrochlore field includes compositions with "excess" B cations that require mixing of some Co on the A sites with Bi 3+ , as found for Zn in all Bi-Zn-Nb-O pyrochlores.…”

“…The considerably larger OЈ displacement in the Co system (0.45 Å) may reflect the higher concentration of smaller B-type ions on the A sites (Ϸ 22 % compared to Ͻ10 % in the Fe system). Displacive models for analogous Bi-Zn-Nb-O [35] and Bi-Mn-Nb-O [37] pyrochlores also displaced A sites to 96g sites (0.39 Å and 0.36 Å, respectively), but OЈ was displaced differently, to 96g sites (0.46 Å for Zn, 0.33 Å for Mn). Differences in the details of the structural displacements are not unexpected, since the local crystal chemistry and any short-range correlations should be affected by different concentrations of small B-type ions on the A sites as well as variations in the concentrations of vacancies on both the A sites and the OЈ sites.…”

“…[29,[35][36][37][39][40][41][42] Refinement with only Bi displaced gave residuals for observed reflections of R f = 0.116 and R w = 0.072 -improved results were obtained when OЈ was also displaced. The A site Bi/Co metals were displaced to six partially filled 96g sites; however, the corresponding 96g position for OЈ was not stable, and difference Fourier maps consistently showed peaks at and around the ideal 8b site (5/8, 1/8, 1/8).…”

“…= 0.237]. The disordered structure was therefore modeled assuming static displacements of the A and OЈ atoms, similar to the analogous Bi-M-Nb-O pyrochlores (M = Zn, [35] Fe, [36] Mn [37] ) whose structures were refined using neutron powder diffraction data. The Bi:Co:Nb ratio of the single crystal was fixed at a stoichiometry inferred from the refined unit cell parameter of ground crystals [a = 10.551(1) Å] taken from the same batch.…”

Synthesis, structure and electrical properties of Mg-, Ni-codoped bismuth niobates

“…The most attention has been paid to the Zn-, Mg-containing bismuth niobates, which possess high dielectric constant (170-180) and low dielectric loss (~10 -4 ) at 1 MHz (at room temperature) [1][2][3][4][5][6][7][8][9]. To search for the same properties Fe- [10], Mn- [11][12], Co- [13], Ni- [12,[14][15], Cu- [12] and the mixed Zn-M (M -Sr [16], Ca [16][17], Mn [16,18], Ti [19][20][21][22], Sn [19,22], Zr [19,[21][22], Ce [19,22], Gd [21], Ta [23], La [24]), Mg-M (M -Sr [25], Nd [26], Cu [27]) bismuth niobates and other ones were synthesized. The improved permittivity was achieved by Ti doping of the Nb sites in the pyrochlore structure [21][22] and by Cu doping in Bi 1.5 Cu x Mg 1-x Nb 1.5 O 7 (x = 0.075) [27].…”