KBiFe 2 O 5 (KBFO) is an upcoming promising brownmillerite-structured multiferroic photoactive material for next-generation photovoltaic and photocatalytic applications. In the present work, KBFO has been developed using multistep thermal treatment method to reduce the volatility of constituent elements and improve the stability of compound. The band gap of KBFO (found to be ∼1.68 eV) extends to the near-infrared region compared to traditional perovskite-structured multiferroics. The magnetic and dielectric transitions occur in the same temperature range (740 K–800 K), reflecting the existence of magneto-dielectric effect in the as-synthesized sample. It also shows promising photocatalytic activity by degrading organic effluents under natural sunlight compared to regular perovskite BiFeO 3 photocatalyst (operating under visible light). A new application of brownmillerite multiferroic KBFO photocatalyst in environmental and energy applications has been explored by integrating the structural, optical, magnetic, and dielectric properties of the same.

We report on the variable range hopping (VRH) crossover in the electrical transport of Sb doped ZnO (SZO) thin film. Structural, chemical, electrical and magnetotransport properties were carried out on SZO thin film grown by pulsed laser deposition. X-photoelectron spectroscopy study confirms the presence of both Sb 3+ (33%) and Sb 5+ (67%) states. Sb doped ZnO thin film shows n-type behavior which is attributed to the formation of Sb Zn and/or Sb Zn -V Zn defect complex. Temperature dependent resistivity measurement showed that in a low temperature regime ( 90 < K) transport is governed by the 3D-VRH mechanism. A crossover from 3D-VRH to Efros-Shklovoski VRH was observed around 12 K. Negative magnetoresistance (MR) is observed in the entire temperature range (300-5 K), however, there is an upturn in the MR behavior at 5 K suggesting the existence of a positive component. The MR behavior of Sb doped ZnO thin films is explained by the Khosla and Fischer model.

Ideal sillenite type Bi12FeO20 (BFO) micron sized single crystals have been successfully grown via inexpensive hydrothermal method. The refined single crystal X-ray diffraction data reveals cubic Bi12FeO20 structure with single crystal parameters. Occurrence of rare Fe4+ state is identified via X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The lattice parameter (a) and corresponding molar volume (Vm) of Bi12FeO20 have been measured in the temperature range of 30–700 °C by the X-ray diffraction method. The thermal expansion coefficient (α) 3.93 × 10–5 K−1 was calculated from the measured values of the parameters. Electronic structure and density of states are investigated by first principle calculations. Photoelectrochemical measurements on single crystals with bandgap of 2 eV reveal significant photo response. The photoactivity of as grown crystals were further investigated by degrading organic effluents such as Methylene blue (MB) and Congo red (CR) under natural sunlight. BFO showed photodegradation efficiency about 74.23% and 32.10% for degrading MB and CR respectively. Interesting morphology and microstructure of pointed spearhead like BFO crystals provide a new insight in designing and synthesizing multifunctional single crystals.

No abstract