Low temperature and broadband dielectric properties of V₂O₅ doped Mg₂TiO₄ ceramics

Abstract

The liquid phase effect of V 2 O 5 on the densification, microstructure and microwave dielectric properties of Mg 2 TiO 4 (MTO) ceramics has been investigated. The addition of V 2 O 5 significantly lowered the sintering temperature compared to pure MTO ceramics with improved microstructure, relative density and microwave dielectric properties. The increase in relative density and average grain size via growth of large grains and dissolution of small grains is explained by Ostwald ripening phenomena. Further, the microwave dielectric properties of the pure and MTO with V 2 O 5 samples were measured at cryogenic temperatures. It was observed that the loss tangent (tan ) and Q × f o of pure MTO increased with temperature, whereas the loss tangent and Q × f o of the samples with V 2 O 5 decreased with a rise in temperature. However, the MTO ceramics added with 0.5 and 1.0 wt% of V 2 O 5 manifested slightly higher loss tangents as compared to the pure MTO ceramics. The mechanism of the microwave loss is in agreement with the theory of intrinsic dielectric loss derived from the two phonon difference process. Further, the distinctive loss peak at 40 K is attributed to the orientation polarization having dispersion at the microwave frequency. The addition of V 2 O 5 did not cause any changes on the temperature stability of the MTO ceramics, whereas the temperature coefficient of the permittivity increases with an increase in temperature. The broadband dielectric measurement reveals that the V 2 O 5 doping increases the dielectric constant and enhances the stability over a wide frequency range, and shows a peak around 1.8 GHz. The tan of pure MTO still shows the peak whereas the samples doped with V 2 O 5 suppresses this peak significantly.

Fundamental mechanisms responsible for the temperature coefficient of resonant frequency in microwave dielectric ceramics

“…A number of other studies have measured τ f using a TE 01δ or TE 011 resonance mode of dielectric resonators16‐22 and assumed that this is equal to τ ε , neglecting the contributions from α L and τ u . From the literature and the measurements reported here, we note that α L can be on the order of 5‐10 ppm/K at 200 K and above for most microwave oxide ceramics, whereas τ u can be of the same order at very low temperature in paramagnetic‐laden dielectrics .…”

“…From the literature and the measurements reported here, we note that α L can be on the order of 5‐10 ppm/K at 200 K and above for most microwave oxide ceramics, whereas τ u can be of the same order at very low temperature in paramagnetic‐laden dielectrics . Since these References16‐22 directly measured τ f , we will only summarize their findings in that light. Subodh et al found that as the temperature increases, the τ f of V 2 O 5 ‐doped Mg 2 TiO 4 dielectrics is ~−30 ppm/K at low temperatures and increases to ~−50 ppm/K above 150 K. An investigation of V 2 O 5 ‐doped Mg 2 TiO 4 ceramics by Bhuyan et al and single‐crystal LaAlO 3 found that τ f is positive at low temperature, increasing slowly as the temperature is raised to ~150‐200 K, then increasing more rapidly above 150‐200 K. Similarly, Pamu et al found that τ f of CuO‐doped Zr 0.8 Sn 0.2 TiO 4 is ~9 ppm/K from 10 to 250 K and then increases significantly up to room temperature .…”

Tweaking Electrical and Dielectric Properties of Nickel Oxide Nanocrystals by Varying the Surfactant

“…and insulin. 17 Studies have demonstrated that physical, chemical, electrical and dielectric properties of nanostructures synthesized through chemical methods can be modified by suitable choice of precursor, 18 solvent typel, 19 surfactants, 20 precipitating agent, 21 22 doping, [23][24][25] processing condition 26 27 and calcination temperature. 28 This can cause a significant change in the microstructure of nanostructures which strongly influence their physical and chemical properties.…”