Development of Bulk and Thin Films of Mg2TiO4 B ased Ceramics for Microwave Applications

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In the present thesis work, we have prepared single phase Mg 2 TiO 4 ceramics by mechanical a nd solid - state reaction methods. The effect of vari ous additives, their concentrations and processing parameters on crystal structure, microstructure and on microwave dielectric properties of MTO ceramics are studied systematically. Successful efforts were made to reduce the sintering temperature from 1450 to 1250 o C without affecting the microwave dielectric properties of the MTO ceramics by reducing the initial particle size and supplementing different types of additives . A maximum relative density of 97.75 % was obtained for the MTO sample sintered at 13 25 o C for 3 hr with best microwave dielectric properties of ε r ~ 13.68, Q×f o ~ 155,000 GHz synthesized by the mechanical alloying method. T he increase in Q×f o values can be attributed to the increase in relative density and identical grain sizes. Further, w ith the addition of CeO 2 nanoparticles, the sintering tempe rature of MTO ceramics is effectively reduced from 1450 to 1300 o C along with the significant improvement in the dens ity and uniform microstructure with highest density of 98.7% (1.5 wt.%) having maximum m icrowave dielectric properties of Q×f o = 167000 GHz and ε r of 14.6. For the samples added with 0.5 wt.% of La 2 O 3 or V 2 O 5 possessed excellent microwave dielectric properties: ε r = 14.3, Q × f o = 157,550 GHz and ε r = 14.4, Q × f o = 168,000 GHz , sintered at 1300 o C and 1250 o C, respectively. In case of MTO ceramics ad ded with 1.0 wt.% of Bi 2 O 3 , exhibited best microwave dielectric properties: ε r = 13.2, Q × f o = 160,500 GHz , sintered at 1250 o C. The obtained excellent microwave dielectric properties of the MTO based ceramics make this material appropriate for type - 1 capa citor and dielectric resonators for various microwave communication applications. Further, microwave dielectric properties of MTO ceramics added with different wt.% of CeO 2 and V 2 O 5 was measured at cryogenic temperatures (6.5 K to 295 K) are found to be ap plicable for cryogenic device applications. In addition, MTO thin films are deposited on various substrates like, Si (100), quartz and platinized silicon (Pt/TiO 2 /SiO 2 /Si)) from the homemade sputtering target by RF magnetron sputtering. The impact of proce ssing parameters (Ar / O 2 ratio) and the post - deposition annealing on structural, microstructural, optical and dielectric properties of MTO films were inves tigated and for the first time, the microwave dielectric properties of pure MTO thin films are studi ed . Furthermore, the microwave dielectric properties of thin films were measured at discrete microwave frequencies, and these properties are comparable to the bulk. Thin films of MTO are suitable for optoelectronic and microwave integrated circuits.
Supervisors: D. Pamu and A. Perumal