Ferrites
LaFeO3 is a multiferroic with multiple functionalities. It demonstrates room-temperature magnetism. A prime interest in this material is to introduce formidable ferroelectricity in LaFeO3 that may improve its functionalities with magnetoelectric properties. Ti4þ has a higher charge and smaller ionic radii. Such changes may modify bond lengths, bond angles, octahedral tilting and oxygen content. As a result, the nature of crystallinity can be modified. As a consequence, the electronic properties like the band gap, transport properties may get influenced. Titanate perovskites are known to be ferroelectric materials.
Intending to strengthen the ferroelectric properties of a magnetic LaFeO3, this work investigates the structural, vibrational and electronic properties of LaFe1-xTixO3 (0 x 0.50). The novelty of this work is on an in-depth study of the bond lengths and bond angles correlated with BO6 octahedra and La8O6 cage distortion. Ti substitution affects the entire perovskite structure by introducing a vertical flattening of the BO6 octahedra as well as the La8O6 cage. The strong hybridization of Ti4þ with O2p may be responsible for such modifications. The locus of octahedral apical oxygen fluctuates, influencing the tilting angle of the BO6 octahedra. This may be a result of the nature of the substituted cations and the oxygen acceptability limit of the lattice. The phonon modes and their modification have been correlated. The transport properties are modified with an external magnetic field.
Manganites
Correlation of octahedral distortion and structural phase transition of multiferroic La(Fe/Mn)O3 solid solution was extensively investigated using x-ray photoelectron spectroscopy (XPS), Raman and x-ray diffraction (XRD) measurements and density functional theory (DFT) calculation. A Pbnm to R3-c phase transformation happens at 62.5% Mn content. The valence state and size of cations influences the octahedral tilting and thereby brings in variations of structural/optoelectronic properties. Octahedral volume is reduced as the entire perovskite structure is relatively flattened with the incorporation of Mn. This implies a flattening of both the BO6 octahedra and the La8O6 cage. The position of the apical oxygen of the BO6 octahedra, i.e. the tilting angle varied with Mn-incorporation. The relative tilting of subsequent octahedra were signified with Glazer representation from the refined Crystallographic Information Files (CIF). A detailed lattice dynamical calculation reveals the effect of distortion on local structure. Modifications in the phonon modes with Mn content have been correlated with structural changes. The electronic properties show a definite trend with Mn concentration in the orthorhombic and rhombohedral phases. This work correlates different structural attributes such as bond lengths, octahedral tilting with electronic and optical properties.