Microstructure, domain structure and phase-transition behavior of alkali niobate-based materials with varying conductivity

Effect of Porosity on the Electrical Properties of Polycrystalline Sodium Niobate: II, Dielectric Behavior

“…As mentioned previously, the phase transition inherent to NaNbO 3 can be modified by either intrinsic 39,44 or extrinsic defects 40 or by manganese doping. 45 Manganese doping causes disorder in the cation sublattice and local strains within the grains, which prevent any movement of the phase front between polar and unpolar microregions.…”

“…Such point defects may cause a strong increase of ε s and a shift of the peak temperature. 39 According to Zhelnova et al, 40 the T m should vary as a function of the stoichiometry in NaNbO 3 , but the specific conductivity of the matrix should increase by five orders of magnitude to reach a shift of Ϫ20°C in T m . However, this was not observed in the conductivity measurements performed above 400°C.…”

“…Domains are created 2,18 at temperatures approaching phase transitions, and the existence of domain walls formed during the phase transition should prevent the phase front from moving through the sample, resulting in a step-like ε s (T) characteristic with a lower transition temperature and an increased dielectric constant during cooling, 43 in agreement with the experimental results shown here. According to Zhelnova et al, 40 it seems that oxygen defects should exert an influence on nucleation and wall motions. Assuming different atomic packing in the related orthorhombic phases, 28 and although the respective influence of oxygen vacancies, cation disorder and internal stresses on the dielectric anomaly investigated is not believed to be predominant, the question of to what extent both the peak temperature and the dielectric constant depend on these factors is still an open one.…”

Effect of Porosity on the Electrical Properties of Polycrystalline Sodium Niobate: I, Electrical Conductivity

“…On the other hand, Zhelnova et al 30 suggested that the semiconductor behavior of alkali niobate based ceramics is due to oxygen deficiency. In the case of NaNbO 3 and KNbO 3 single crystals, an anomalous increase in conductivity was observed after reduction under vacuum and/or dc polarization.…”

Room Temperature Ferroelectricity in Na1−xSrx/2◻x/2NbO3 through the Introduction of Cationic Vacancies

“…In addition to the isovalent doping process, chemical substitutions leading to controlled nonstoichiometric compounds have been performed. In this way, Na 1− x NbO 3− x /2 oxides and NaNbO 3− x have been prepared to analyze the influence of the partial reduction of Nb(V) on the variation of the maximum temperature permittivity. However, the creation of a certain amount of oxygen vacancies does not modify the antiferroelectric character of sodium niobate.…”