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

Abstract

Synthesis, structure and electrical properties of Mg-, Ni-codoped bismuth niobatesMg-, Ni-codoped bismuth niobates Bi 1.6 Mg 0.8-x Ni x Nb 1.6 O 7-δ (x = 0; 0.2; 0.4; 0.6; 0.8) were obtained by conventional solid-state reaction method. It was shown that the Mg atoms are distributed at the Nb sites while the Ni atoms are distributed over the Bi-and the Nb-sites, according to the results of comparison of pycnometric and X-ray density of the Bi 1.6 Mg 0.4 Ni 0.4 Nb 1.6 O 7-δ pyrochlore. In this case, about 15-20% of the vacancies are formed at the Bi sites. The obtained compounds are stable up to their melting point based on the DSC analysis data. Real dielectric permittivity ε' of the Bi 1.6 Mg 0.8-x Ni x Nb 1.6 O 7-δ samples decreases from 80 to 65 with the temperature decrease from 25 to 700 °C and practically does not depend on frequency in the range of 1-1000 kHz. Oxides Bi 1.6 Mg 0.8-x Ni x Nb 1.6 O 7-δ behave like insulators up to 280 °C, their conductivity increases with temperature (E a,dc ≈ 1.3 eV, dc) and with the Ni content at a given temperature.

Structure, thermal stability, optoelectronic and electrophysical properties of Mg- and Na-codoped bismuth niobate pyrochlores: Experimental and theoretical study

“…The narrowest "pyrochlore field" is characteristic for nickel-or zinccontaining bismuth niobates [2,25,27], and the largest is typical for manganese-and ironcontaining compounds [13,26]. Besides this, two types of dopants can be distributed simultaneously in the pyrochlore structure [28][29][30][31][32][33][34][35]. The complex structure of pyrochlore-type niobates led to a series of structural studies of cationic distribution using neutron powder diffraction [2,13,14,26,36,37].…”

“…The proton transport is a characteristic feature for defective pyrochlore structures detected up to 500-700 °C [30,47,48]. From the data of temperature-J o u r n a l P r e -p r o o f 4 programmed isotope exchange (TPIE) with C 18 O 2 in closed and flow reactors, activation of oxygen transport starts from 250 °C [35] but obeys the Arrhenius law (lgσ = f(10 3 /T)) at T > 360-400 °C [30,34].…”

Dielectric Properties of Bi₄(Ti,Nb,Mn)₃O₁₂ Titanates

“…At temperature gaining the peak on the M′′ = f(ν) dependencies shifts towards higher frequencies, which implies that dielectric relaxation in Bi 4 Ti 2.7 Nb 0.15 Mn 0.15 O 12 is thermally activated. A slight asimmetry of the M′′ peaks is observed and the magnitude of the width of the peaks at their half-maxima is larger than ideal Debye response (1.14 decades), which shows that relaxation processes in the ceramics are, probably, of non-Debye type [20,21]. The low values of M′′ at low frequencies indicate that contribution of electrode processes in the polarization of material is negligible.…”