Effect of Mn doping on dielectric response and optical band gap of LaGaO ₃

In order to realize the effect of Mn doping on dielectric behavior and optical band gap (E _g ) of Lanthanum Gallate; pure and Mn doped LaGaO ₃ samples were prepared. The phase purity of these samples was confirmed by x-ray diffraction experiments. It was found that all samples possess orthorhombic structure. Room temperature (RT) dielectric response and E _g of LaGa _1−x Mn _x O ₃ (LGMO) with, x = 0.0 to 0.9, has been recorded using impedance analyzer (LCR meter) and diffuse reflectance spectroscopy respectively. It has been observed that at RT, pure LaGaO ₃ exhibits moderate dielectric constant (ε′ ≈ 25) with very low dielectric loss (tan δ). Interestingly, the value of RT ε′ significantly increases with Mn doping whereas tan δ remains relatively low upto x = 0.4 and increases abruptly x > 0.4. The observed increase in ε′ and tan δ with Mn doping has been understood in terms of structural coherency and systematic decrease in E _g . A shift in ε′-anomaly (tan δ-peak) with increasing Mn percentage and low frequency large ε′ were also observed in Mn doped LGO. Both of these effects have been understood in terms of coexisting Mn ³⁺ and Mn ⁴⁺ ions. The LGMO samples (x ≤ 0.4) showing high value of ε′ and very low tan δ can be suitable candidates for capacitive applications.