Structural, Optical, and Dielectric Properties of A[(Mg0.32Co0.02) Nb0.66]O3 Semiconductor, Where (a = Ba, Sr or Ca)

Author(s) B. Bishnoi1, P.K. Mehta1 , C.J. Panchal2 , M.S. Desai2 , R. Kumar3

1 Department of physics, Faculty of Science, The M.S. University of Baroda, Vadodara-390002, Gujarat, India

2 Applied Physics Department, Faculty of Technology & Engineering, The M.S. University of Baroda, Vadodara-390001, Gujarat, India

3 Head, Material Science Division, National Institute of Technology, Hamirpur-177005, Himachal Pradesh, India

Issue Volume 3, Year 2011, Number 1, Part 4
Dates Received 04 February 2011, in final form 14 October 2011, published online 17 October 2011
Citation B. Bishnoi, P.K. Mehta, C.J. Panchal, M.S. Desai, R. Kumar, J. Nano- Electron. Phys. 3 No1, 698 (2011)
PACS Number(s) 77.22. – d, 77.22.Ch, 77.22.Gm
Key words X-ray diffraction (18) , Band Gap (25) , Dielectric properties (5) , AC conductivity (3) , 1:2 niobates.
Structural optical and dielectric properties of single phase A[(Mg0.32Co0.02) Nb0.66]O3, where A = Ba, Sr, or Ca, compounds were studied in the temperature range from room temperature (293 K) to 458 K. The X-ray diffraction revealed that the Ba[(Mg0.32Co0.02)Nb0.66]O3 [BMCN] compounds exhibit hexagonal symmetry whereas Sr[(Mg0.32Co0.02)Nb0.66]O3 [SMCN] and Ca[(Mg0.32Co0.02)Nb0.66]O3 [CMCN] compounds exhibit monoclinic symmetry. The replacement of Barium (r =1.61 Å) by smaller ions like Strontium (r = 1.44 Å) or Calcium (r = 1.34 Å) in the polar dielectric Ba[(Mg0.32Co0.02) Nb0.66]O3 introduces the relaxation phenomenon and a gradual increase in the transition temperature maximum (Tm). The ac conductivity, as determined from the dielectric data, as a function of temperature and frequency, reveals the crossover from small polaron tunneling (SPT) to correlated barrier hopping (CBH) type conduction at ≈ 370 K. The activation energy of the non-Debye type process evaluated both from the electric modulus and the conductivity data are nearly identical suggesting similarity in the hopping mechanism. The band gap of these materials lies in the range of narrow to wide band semi conductors.