Detailed Phase Analysis and Crystal Structure Investigation of a Bi_1−xCa_xFeO_3−x/2 Perovskite-Related Solid Solution Phase and Selected Property Measurements Thereof

Abstract

A well-ordered, perovskite-related, Bi 1-x Ca x Fe III O 3-x/2 solid solution phase is synthesized via a rapid liquid phase sintering technique and shown to exist over the composition range ∼0.20<x<∼0.49. Two phase regions are shown to separate this phase from compositionally narrow end-member Bi 1-x Ca x Fe III O 3-x/2 solid solutions based on rhombohedral BiFeO 3 and brownmillerite, Ca 2 Fe 2 O 5 , respectively. The wide range, non-stoichiometric phase is characterized by a well ordered, (in general) incommensurately modulated structure that varies systematically with composition. M :: ossbauer spectroscopy is used to verify the oxidation state of iron as (III), as well as showing the existence of three separate iron environments across the solid solution field. HRTEM imaging is used to develop a structural model for the phase at one particular composition. The magnetic, dielectric, and impedance properties of this solid solution phase are reported. Magnetic measurements show antiferromagnetic behavior. There is no change in either susceptibility or antiferromagnetic behavior with composition. Attempts at obtaining saturated ferroelectric loops failed due to high intrinsic conductivity. The phase is found to exhibit a low frequency impedance relaxation that is likely due to correlated oxygen vacancy hopping.

Mn substitution-induced revival of the ferroelectric antiferromagnetic phase in Bi1−x Ca x FeO3−x/2 multiferroics

“…One can see that compositional dependence of the lattice parameters in the rhombohedral phase deviates from a Vegard-type character expected for solid solutions (Fig. 2a) to be consistent with a complex structural state characteristic of the y = 0 samples [20,26,27]. Indeed, previous transmission electron microscopy measurements of this compound found a complicated behavior suggesting coexistence of the rhombohedral and two incommensurately modulated phases distinguished by the oxygen vacancies concentration [27].…”

“…1a). The parent compound, Bi 0.9 Ca 0.1-FeO 2.95 , was confirmed to exhibit a broadening of the Bragg peaks [19,20], which is supposed to be associated with a nanoscale coexistence of the competing structural phases near the ferroelectric-nonferroelectric phase boundary in the Bi 1-x Ca x FeO 3-x/2 system [26,27]. The broadening disappears upon Mn substitution (inset in Fig.…”

The influence of Mn substitution on the local structure of Na0.5Bi0.5TiO3 crystals: Increased ferroelectric ordering and coexisting octahedral tilts

“…5 Doping is known to modify the crystal structure and improve material properties: examples include La and K in PZT, [36][37][38][39] Sr and Ta in NaNbO 3 , [40][41][42][43] and Ca and Sm in BiFeO 3 . [44][45][46][47][48] Crystals of Mn-doped NBT have been reported to have: (i) enhanced resistivities, remnant polarizations, coercive fields, and d 33 values; (ii) a slight decrease in the phase transformation temperatures; and (iii) a decrease in the size of the T ferroelastic domains. 49 It is noted that the addition of Mn has little effect on the properties of NBT ceramics at room temperature, 50 which might indicate subtle differences between crystals and ceramics, possibly due to changes in stress accommodation of domains.…”

Decomposition behavior and dielectric properties of Ti-doped BiFeO3 ceramics derived from molten salt method

“…One is with the help of leaching out the impurity by the diluted nitric acid [11]. Other research work involves the formation of solid solutions between the BiFeO 3 and other ABO 3 perovskites, or the Bi/Fe-site doping [12][13][14]. The alternatively method to obtain the pure BiFeO 3 phase is the complex solution processes, such as hydrothermal synthesis [15], sol-gel [16], and polymerized complex [17].…”

“…Wang et al [6] has reported the rapid liquid phase sintering is effective way to obtain the BiFeO 3 ceramics with single phase and saturated ferroelectric polarization. Other research work proves that the formation of solid solutions between the BiFeO 3 and other ABO 3 perovskites, or the Bi/Fe-site doping can hinder the impurity phase formation and enhance the resistivity [12][13][14]. As for the Fe-site doping, Ti-doping has been reported to improve the synthesis and ferroelectricity of BiFeO 3 film or ceramics [7,12,20].…”