The thermodynamic stability of BiFeO3 is investigated by high temperature X-ray diffraction and isothermal heat treatment of Bi2O3−Fe2O3 powder mixture as well as phase pure BiFeO3 prepared by a wet chemical route. Experimental evidence for decomposition of BiFeO3 to Bi25FeO39 and Bi2Fe4O9 in the temperature interval 720−1040 K is reported. The experimental observations are discussed in terms of available thermodynamic data for the system. Finally, the stability of BiFeO3 and related Bi-based perovskites is discussed in relation to Goldschmidt tolerance factor and the influence of pressure and chemical substitution.

BiFeO3 nanoparticles prepared by a modified Pechini method display strong size-dependent properties. The rhombohedral distortion from cubic structure is reduced by decreasing particle size accompanied by decreasing polarization inferred from atomic displacements found by Rietveld refinement of X-ray powder diffraction data. With decreasing crystallite size, the Néel temperature decreased and the magnetic transition was increasingly diffuse. The Néel temperature was shown to correlate with the volume of the crystallites and the polar displacements of cations.

Nanorods, nanowires, and nanotubes of ferroelectric perovskites have recently been studied with increasing intensity due to their potential use in non-volatile ferroelectric random access memory, nano-electromechanical systems, energy-harvesting devices, advanced sensors, and in photocatalysis. This Review summarizes the current status of these 1D nanostructures and gives a critical overview of synthesis routes with emphasis on chemical methods. The ferroelectric and piezoelectric properties of the 1D nanostructures are discussed and possible applications are highlighted. Finally, prospects for future research within this field are outlined.

BiFeO3 displays an abrupt first order transition from the polar structure R3c to centrosymmetric $R\bar 3c$ at TC = 830 °C. The ferroelectric transition is associated with abrupt changes in polar cation displacements and a large discontinuous volume. A continuous volume expansion occurs across the second order antiferromagnetic transition at TN = 370 °C. Electronic conductivity anomalies are associated with both phase transitions.

Crystal structure and thermal properties of La1−xSrxFeO3−δ (x= 0, 0.1, 0.3, 0.4, 0.5, and 0.75) have been studied by high‐temperature X‐ray diffraction and thermal analysis in air and nitrogen (p(O2) ∼ 10−3 atm) atmosphere. The first‐order phase transition from orthorhombic‐to‐rhombohedral La1−xSrxFeO3−δ (x= 0, 0.1) was strongly shifted to lower temperatures with increasing Sr content. The phase‐transition temperature was observed significantly lower in polycrystalline ceramics compared with fine powders. The temperature depression of the phase transition in the ceramics was qualitatively explained by stresses induced both by the anisotropic thermal expansion of LaFeO3 and the observed volume contraction of the phase transition. Rhombohedral La1−xSrxFeO3−δ (x= 0.3, 0.4, 0.5) were observed to transform to the cubic perovskite structure during heating. The second‐order phase‐transition temperature decreased with increasing Sr content and decreasing partial pressure of oxygen. On the basis of the present findings, a pseudobinary phase diagram of the LaFeO3–SrFeO3−δ system is presented. Finally, a severely nonlinear thermal expansion was observed for the Sr‐rich materials at high temperature. The high thermal expansion in this region is due to a chemical expansion resulting from a reduction of the valence state of Fe.

The synthesis of phase-pure BiFeO 3 has been demonstrated by a chemical synthesis route as well as the solid-state method at 8251C. Polymeric BiFeO 3 precursors were obtained from aqueous solutions of nitrate salts and carboxylic acids with and without ethylene glycol added as a polymerization agent. The polymeric precursors were shown to decompose above 2001C with successive nucleation and growth of BiFeO 3 above 4001C. The phase purity of the product was shown to depend on the type of carboxylic acid used, and tartaric, malic, and maleic acids resulted in nanocrystalline phase-pure BiFeO 3 . The unit cell and Ne´el temperature of the bulk materials obtained by the two methods were in accord with previous reports.

Nanocrystalline cerium oxide based powders (CeO2, (GdO1.5)0.2(CeO2)0.8, and (SmO1.5)0.2(CeO2)0.8) have been produced using combustion synthesis with glycine as fuel and nitrate as oxidizer. The pure CeO2 powders prepared by using different glycine-to-nitrate ratios have been characterized by X-ray diffraction (crystallite size), thermogravimetry, infrared spectroscopy, surface area analysis, and transmission electron microscopy. The influence of calcination temperature on crystallite size, surface area, and carbonate species remaining from the combustion reaction has been studied especially for the near stoichiometric glycine/nitrate ratio (G/N = 0.55) to reveal the optimal synthesis conditions for all three compositions. A G/N ratio of 0.55 and calcination at 550 °C in oxygen flow gave high quality powder with a crystallite size of ∼10 nm. The powders had excellent sintering properties with an onset of densification at ∼600 °C.

The structure and properties of materials in the BiFeO 3 -rich side of the pseudo-binary phase diagram BiFeO 3 -BiMnO 3 are reported. Manganese substitution (x) and oxygen hyperstoichiometry (δ) are demonstrated to strongly affect the crystallographic properties, electrical conductivity, and phase-transition temperatures of BiFe 1-x Mn x O 3þδ . Increasing the manganese content and oxygen hyperstoichiometry of the materials depresses the N eel temperature, the ferroelectric Curie temperature, and the transition temperature from the paraelectric, ferroelastic structure to the paraelastic, cubic perovskite structure. The thermodynamics of the ambient pressure solid solubility is discussed and a phase diagram for the system BiFe 1-x Mn x O 3þδ is presented, establishing the stability regions of three, two, one, and zero simultaneous ferroic properties. Finally, technological implications of the influence of manganese and excess oxygen are discussed.