Influence of Mn doping on dielectric properties, conduction mechanism and photocatalytic nature of gadolinium-based orthochromites

Abstract

The samples of manganese (Mn)-doped gadolinium chromite [GdCr1−xMnxO3 (x = 0, 0.1, 0.2 and 0.3)] are prepared through sol–gel auto combustion route. The influence of Mn-doping in GdCrO3 is studied in respect of structural, dielectric, electrical and photocatalytic studies. Raman spectra assured the formation of single-phase orthorhombic structure with Pbnm space group and Raman vibration modes for GdCrO3 shift on Mn doping which may be attributed to the influence of the lattice strain, defects, and crystallite size. Dielectric constant (e′), dissipation factor (tanδ) and AC conductivity (σac) are investigated as a function of frequency as well as temperature. Dielectric constant, energy dissipation factor and AC conductivity of pristine sample GdCrO3 show relatively higher values but these values decrease with the increase in Mn doping. The dielectric constant as a function of temperature for all the investigated samples peaks around 250 °C which may be attributed to the high temperature phase transformation. These peaks are observed to shift toward lower temperature with the increase in Mn-doping. The enhancement in AC conductivity is noticed for all the samples with the rise in temperature for the probing frequencies. The non-overlapping small polaron tunneling (NSPT) and correlated barrier hopping (CBH) models dominate the conduction mechanism in these samples. An increase in the experimental values of the hopping energy is observed with the increase Mn concentration for CBH as well as NSPT models. A systematic reduction in activation energy with frequency is noticed for all the samples except for GdCr0.9Mn0.1O3 sample. Real (Z′) and imaginary (Z″) values of impedance are found to reduce with the increase in frequency up to a certain limiting range and then become almost frequency independent at higher frequencies. Nyquist plots of the samples show single semicircular behaviour that indicates the dominance of grain boundary resistance as compared to grain resistance in this system. The grain and grain boundary resistances are determined, with the help of equivalent circuit designed using Zview software, to study the contribution of the grains and grain boundaries to the conductivity. Photo-degradation of Congo red dye under visible light irradiation was used to investigate the photocatalytic activity of the GdCrO3 and GdCr0.9Mn0.1O3 samples. The results confirmed that the catalytic function of the GdCrO3 enhances on Mn doping.