Effect of Mn doping on dielectric response and optical band gap of LaGaO₃

Abstract

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 LaGaO₃ 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−xMn_xO₃ (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 LaGaO₃ 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 Mn³⁺ and Mn⁴⁺ ions. The LGMO samples (x ≤ 0.4) showing high value of ε′ and very low tan δ can be suitable candidates for capacitive applications.

Keywords:

• Lanthanum gallate
• dielectric constant
• dielectric loss
• band gap
• diffuse reflectance spectroscopy

Acknowledgments

Authors sincerely thank Prof. P. Mathur, Director of IIT Indore, for his encouragement. The authors are thankful to Dr Archna Sagdeo (SOE, RRCAT Indore) for XRD measurements. CSIR, New Delhi is acknowledged for funding high temperature furnace under the project 03(1274)/13/EMR-II used for the sample preparations. DAE-BRNS is acknowledged for funding Impedance Analyzer used for the present measurements under the grant No. 2013/37P/31/BRNS. One of the authors (HMR) acknowledges the Ministry of Human Resource Development (MHRD), government of India for providing financial support as Teaching Assistantship.