We report here the synthesis and dielectric characteristics of lead-free methylammonium bismuth chloride (MABiCl) and bromine (Br) doped methylammonium bismuth chloride (MABiBrCl) powders. The dielectric characteristics of the samples (pressed powder pellet) measured in the frequency range 1 Hz to 1 MHz and temperature range 333–403 K indicate complex electrical transport in these halide perovskite materials. We have observed that the transport is dominated by longrange hopping of carriers and localized charges above and below a critical frequency respectively. The experimental data are fitted with the theoretical models considering grains, grain boundary, and contacts effects and made a comprehensive analysis. The activation energy obtained from ac electrical conductivity measurements is found to be relatively higher for the Br doped MABiBrCl than undoped MABiCl, which might explain some of the properties reported on solar cells and optoelectronic devices.
@article{chandra_dielectric_2022,title={A dielectric study of {Br}-doped lead-free methylammonium bismuth chloride ({CH3NH3}){3Bi2BrxCl9}−x},volume={128},copyright={All rights reserved},issn={0947-8396, 1432-0630},doi={10.1007/s00339-022-05677-9},language={en},number={6},urldate={2022-06-01},journal={Applied Physics A},author={Chandra, Paramesh and Saha, Saroj and Mandal, Swapan K.},month=jun,year={2022},keywords={Chemical synthesis, Dielectric relaxation, Impedance spectroscopy, Perovskite},pages={541},}
Mat. PHYSICA B
Spin state bistability in (Mn, Zn) doped Fe(phen)2(NCS)2 molecular thin film nanocrystals on quartz
Spin state bistability within high spin (HS) and low spin (LS) state is investigated in undoped and (Zn, Mn) doped spin crossover (SCO) complex Fe(phen)2(NCS)2 thin films (thickness ∼ 300 nm) deposited by dip-coating technique at room temperature on the quartz substrate. The X-ray diffraction studies clearly show the formation of crystalline structure of SCO complexes. The growth of the thin films was indisputably confirmed by electron microscopy and optical studies. The optical absorption peak between 535-557 nm was clearly observed, and that corresponds to 1A1g → 1T1g ligand field absorption in undoped and metal-doped (Zn, Mn) SCO thin films. The high spin (HS) state of the SCO films at room temperature was confirmed by Raman spectra. The bistability of spin states is clearly revealed by the well pronounced thermal hysteresis loop in magnetization measurements. The spin transition temperature (T1/2) and loop width are found to be critically dependent on metal doping and suggested the possibility of tuning these parameters in spin-crossover thin films to design future spin-based devices.
Mater. Today
Frequency and temperature-dependent dielectric characteristics of lead-free Br doped perovskites (CH3NH3)3Bi2Cl9 and (CH3NH3)3Bi2BrxCl9-x
Chandra, Paramesh, Saha, Saroj, and Mandal, Swapan
We report the synthesis and dielectric characteristics of lead-free methylammonium bismuth chloride (MABiCl) and Br doped methylammonium bismuth chloride (MABiBrCl) in powder form. The morphology of the samples showed growth of large flakes with large surface area. The band gaps of the perovskites are obtained from optical absorption data. The dielectric characteristics of the samples were measured in the frequency range 1 Hz to 1 MHz and temperature range 100–300 K. The data shows a complex electrical transport in these halide perovskite materials. The dielectric permittivity data shows the existence of a critical temperature at which the material undergoes a structural phase transition. The transition temperature is found to be 270 K and 266 K for MABiCl and MABiBrCl respectively. The results can be explained by certain change in orientation of methyl-ammonium (MA) ions as the temperature is increased.
@article{chandra_frequency_2022,title={Frequency and temperature-dependent dielectric characteristics of lead-free Br doped perovskites ({CH}3NH3)3Bi2Cl9 and ({CH}3NH3)3Bi2BrxCl9-x},author={Chandra, Paramesh and Saha, Saroj and Mandal, Swapan},date={2022-07-06},doi={10.1016/j.matpr.2022.06.413},journal={Materials Today: Proceedings},note={Journal Abbreviation: Materials Today: Proceedings
Publication Title: Materials Today: Proceedings},}
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