Observation of Griffiths Phase, Critical Exponent Analysis and High Magnetocaloric Effect Near Room Temperature at Low Magnetic Field in V doped La0.7Sr0.3MnO3

We report on observation of Griffiths phase, high magnetocaloric properties at low magnetic fields and temperature dependent critical exponents of La0.7Sr0.3VxMn1-xO3 (x=0, 0.05 & 0.1) perovskite bulk materials. The Curie temperature (TC) of pure La0.7Sr0.3MnO3 is seen to be 368.7 K and decreases towards room temperature (342.2 K) by 10 mol% vanadium doping at the Mn site. Vanadium doping leads to enhancement in magnetic entropy change (-SM) from 1 Jkg-1K-1to 1.41 Jkg-1K-1. Vanadium doping at Mn site leads to the formation of Griffiths phase, a magnetic disorder due to the co-existence of paramagnetic matrix and short range ferromagnetic clusters. X-ray photoelectron spectroscopy analysis confirm the presence of mixed valance V4+/V5+along with Mn3+/ Mn4+ ions contributing to various double exchange interactions. Nature of phase transitions and magnetic interactions are analyzed by evaluating critical exponents and. All the samples show second-order ferromagnetic (FM) to paramagnetic (PM) phase transition, confirmed from the modified Arrott’s plots and critical exponent analysis carried out using Kouvel-Fisher method. Enhancement in magnetic entropy change along with the decrease in Curie temperature towards room temperature by vanadium doping in the La0.7Sr0.3MnO3 oxides indicates the possible application of these materials for the magnetic refrigeration at low magnetic fields.

Synthesis of Vanadium Doped Lanthanum Bismuthate Nanorods for Enhanced Photocatalytic Activity

Vanadium doped lanthanum bismuthate nanorods with vanadium ratio of 1%, 3%, 5% and 10 wt.% were fabricated through the hydrothermal method using sodium orthovanadate as vanadium source. Vanadium doped lanthanum bismuthate nanorod products were analyzed by scanning electron microscopy, X-ray diffraction pattern and diffuse reflection spectrum. X-ray diffraction patterns show that vanadium in the vanadium doped lanthanum bismuthate nanorods exists as triclinic Bi23V4O44.5 and monoclinic LaVO4 phases. Scanning electron microscopy observations show that the size and micro-morphology of the vanadium doped products are closely relative to the vanadium mass ratio. The length of the vanadium doped nanorods decreases and the morphology changes from nanorods to irregular nanoparticles with increasing the vanadium mass ratio. Solid UV-vis diffuse reflectance measurement shows that the bandgap value of the doped lanthanum bismuthate nanorods is narrowed from 2.37 eV to 2.25 eV after the vanadium doping ratio is increased from 1% to 10%. The doped lanthanum bismuthate nanorods illustrate enhanced photocatalytic performance for methylene orange (MO) removal with the irradiation of sunlight. The catalytic performance for MO removal depends on the irradiation time, vanadium content and dosage of the nanorods. The doped lanthanum bismuthate nanorods with the vanadium mass ratio of 10% possess the best MO catalytic degradation performance.