Doping Effects of Ta on Conductivity and Microwave Dielectric Loss of MgTiO₃ Ceramics

Abstract

Two kinds of solid solution systems of Ta‐doped MgTiO3 were identified by X‐ray diffraction, which can be represented by the formulae MgTi1−x(Mg1/3Ta2/3)xO3 (0≤x<0.5) and MgTi1−xTaxO3 (0≤x<0.05). The conductivity and microwave dielectric loss for the two solid solution systems were examined by AC impedance and microwave resonator measurements, respectively. In the system MgTi1−x(Mg1/3Ta2/3)xO3, the mechanism for the solid solution formation is the isovalent substitution of for Ti4+. In the system MgTi1−xTaxO3, the doping mechanism is the aliovalent substitution of Ta5+ for Ti4+, where for a small amount Ta doping, the oxygen vacancies formed during the high‐temperature preparation are filled by an extra oxygen introduced from Ta2O5 and further Ta doping leads to an increase in the contents of and electrons, which was consistent with conductivity measurements. In both systems, the Q×f values improved, e.g., ∼17% for the isovalent substitution at x=0.08 and ∼10% for the aliovalent substitution at x=0.02. The filling oxygen vacancy and the substitution of Ta/Mg for Ti may contribute to the improvement of Q×f values for both systems.

Dielectric characteristics of the (1−x)Mg2TiO4–xSrTiO3 ceramic system at microwave frequencies

“…On the other hand, high quality factor (inverse of the dielectric loss, Q = 1/tan ␦) would play a more prominent role instead, since Q × f is almost constant in the microwave region [2]. It explained the research on high-Q dielectric materials, such as the MgO-TiO 2 binary system, has brought much more attention recently [3][4][5][6]. Among these compositions, MgTiO 3 and Mg 2 TiO 4 are both recognized as good candidates for high frequency applications.…”

Determining the Quality Factor of Dielectric Ceramic Mixtures with Dielectric Constants in the Microwave Frequency Range

“…As a result, only the tendency of dielectric constant variation can be roughly estimated if the molecule or ion with non-cubic symmetry 2,5,35 . The quality factor change of the ionic substitution is usually attributed to the grain size 20,21,23 , porosity 11,12 , structure 24 , phase evolution 5 , internal strain 2,36–38 , material conductivity 39 and so on. Huang 10 et al .…”

“…Ohsato 37 linked the quality factor to the internal strain based on the work of Stokes 38 et al . Kuang 39 evaluated the quality factor by estimating the materials’ conductivity at microwave frequency. In all these reports, quality factor trends agree with the grain size, phase evolution, porosity, internal strain, and conductivity 5,6,10,27,37–39 .…”

PHASE EVOLUTION AND MICROWAVE DIELECTRIC PROPERTIES OF Ca0.61Nd0.26Ti1-x (Al1/2Nb1/2)xO₃ CERAMICS (0 ≤ x ≤ 0.2)

“…The grain boundary could act as a two-dimension defect interrupting the symmetry of the crystal, thus smaller grain size, in other words, more defects, will give rise to lower Q × f [10]. Also, the increment of electrons (Nb 5+ donor doping), resulting from high content doping: Nb 2 O 5 TiO 2 ·2Nb Ti + + 4O o x + ½O 2 + ↑2e [18,20] was another factor causing the decrease of Q × f. It has been reported that dielectric loss was proportional to conductivity, tan δ σ, so that too much substitution would lead to low Q value [18,20]. The substitution at Ti 4+ site slightly changed lattice parameters that influenced the degree of tilting of octahedral [10].…”