Abstract
Giant dielectric (GD) oxides exhibiting extremely large dielectric permittivities (ε’ > 104) have been extensively studied because of their potential for use in passive electronic devices. However, the unacceptable loss tangents (tanδ) and temperature instability with respect to ε’ continue to be a significant hindrance to their development. In this study, a novel GD oxide, exhibiting an extremely large ε’ value of approximately 7.55 × 104 and an extremely low tanδ value of approximately 0.007 at 103 Hz, has been reported. These remarkable properties were attributed to the synthesis of a Lu3+/Nb5+ co-doped TiO2 (LuNTO) ceramic containing an appropriate co-dopant concentration. Furthermore, the variation in the ε’ values between the temperatures of −60 °C and 210 °C did not exceed ±15% of the reference value obtained at 25 °C. The effects of the grains, grain boundaries, and second phase particles on the dielectric properties were evaluated to determine the dielectric properties exhibited by LuNTO ceramics. A highly dense microstructure was obtained in the as-sintered ceramics. The existence of a LuNbTiO6 microwave-dielectric phase was confirmed when the co-dopant concentration was increased to 1%, thereby affecting the dielectric behavior of the LuNTO ceramics. The excellent dielectric properties exhibited by the LuNTO ceramics were attributed to their inhomogeneous microstructure. The microstructure was composed of semiconducting grains, consisting of Ti3+ ions formed by Nb5+ dopant ions, alongside ultra-high-resistance grain boundaries. The effects of the semiconducting grains, insulating grain boundaries (GBs), and secondary microwave phase particles on the dielectric relaxations are explained based on their interfacial polarizations. The results suggest that a significant enhancement of the GB properties is the key toward improvement of the GD properties, while the presence of second phase particles may not always be effective.
Highlights
An effort to develop giant dielectric (GD) materials has been driven by an increased demand for high-energy-density storage devices in the electronic industry [1]
We firstly report the influences of microstructure and second phase particles on the Giant dielectric (GD) properties of a co-doped TiO2 system of Lu3+ /Nb5+ (LuNTO) ceramics
The extremely low tanδ value of approximately 0.007 exhibited by the Lu3+/Nb5+ co-doped TiO2 (LuNTO)-1 ceramic at 1 kHz and 30 ◦ C is attributed to the ultra-high resistivity exhibited by the internal insulating regions, i.e., the grain boundaries (GBs) and secondary-phase particles corresponding to the LuNbTiO6 microwave-dielectric phase
Summary
An effort to develop giant dielectric (GD) materials has been driven by an increased demand for high-energy-density storage devices in the electronic industry [1]. A novel elegant GD material, In3+ /Nb5+ co-doped TiO2 , was reported to exhibit an ε’ > 104 and a tanδ < 0.05 [9] This material exhibited stable dielectric properties with respect to the frequency and temperature across a wide range of values. We firstly report the influences of microstructure and second phase particles on the GD properties of a co-doped TiO2 system of Lu3+ /Nb5+ (LuNTO) ceramics. The highest dielectric performance exhibited by a LuNTO ceramic recorded a very high ε’ value of approximately 7.5 × 104 , while exhibiting excellent temperature stability between 60 ◦ C and 210 ◦ C and a very low tanδ value of approximately 0.007. The tanδ value exhibited at 200 ◦ C (approximately 0.05) was acceptable
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