Ludong Ji

Raman and dielectric response of BaTi1-x(Mg1/3Nb2/3)xO3 solid solution

Structural evolution and dielectric analysis have been performed for BaTi1-x(Mg1/3Nb2/3)xO3 solid solutions with x ≤ 0.07, together with the analysis of Raman spectroscopy. X-Ray diffraction and Raman results show a structural evolution from a tetragonal phase to a cubic one with increasing x. Dielectric analysis reveals a low critical concentration corresponding to ferroelectric–relaxor crossover (xc = 0.05). Activation energy with dozens meV is obtained using the Vogel–Fulcher relationship, which is attributed to thermally activated off-center ion hopping.

Dielectric Response of Ba0.5Sr0.5TiO3-Mg2SiO4 Composites Synthesized by a Citrate Gel In-Situ Process

(1-x)Ba0.5Sr0.5TiO3(BST)-xMg2SiO4 (MS) composite ceramics have been synthesized in-situ via a citrate-nitrate combustion process, and their structure and effective dielectric response have been investigated. The compositions with x ≥ 0.3 formed a second phase Ba2TiSi2O8, besides BST and MS phases. The BST-MS composites showed an uniform microstructure with MS particles homogeneously dispersed in BST particles. The temperature at the permittivity maxima of the composites was nearly unchanged with increasing the volume fraction of MS (ƒMS) from 0.1 to 0.4 and then slightly decreased with further increasing ƒMS. According to the modified effective medium approx-imation couple with the spherical inclusion model, the permittivity (ϵBST) of BST in the composites was strongly dependent on ƒMS, which was defined by the relation .

Controllable-permittivity and low-loss of Ba0.5Sr0.5TiO3/MgO composites prepared by citrate gel derived core-shell powders

Core-shell Ba0.5Sr0.5TiO3(BST)/MgO nano-composites have been synthesized by using an oleic acid modified citrate gel in situ process. The nano-composites exhibit a spherical microstructure consisting of large amounts of small particles with average sizes of 50-100 nm, which results in high F center levels in the composite ceramics. Interestingly, microwave permittivity of the composite can be reduced significantly with increasing volume fraction of MgO, while microwave loss and tunability remain almost unchanged, which is in good agreement with the results of the columnar model.