Advances in Science and Technology Vol. 118

Abstract: In this work, the effect of mechanochemical synthesizing method on the properties of the Li₇La₃Ce₂O₁₂ was studied. The Li₇La₃Ce₂O₁₂ was prepared using planetary ball-mill method heated at 900 °C with intermittence grinding. The X-ray diffraction analysis shown that the sample exhibited tetragonal structure at room temperature with space group I4/mmm. An incomplete single semicircle arc was observed in the complex impedance shows that the sample was contributed by bulk effect and need a much higher frequency to measure the impedance response. The conductivity of the samples exhibits temperature dependence at lower temperature and frequency dependence at much higher temperature which associated to the ionic conductor behavior. Two slopes were observed from the activation energy plot indicates that more likely electron and ionic transport within the sample.

Abstract: The Li₇La₃Ce₂O₁₂ ceramic was synthesized in this work by using a conventional solid-state reaction route and a planetary ball-mill method. At room temperature, the sample had a tetragonal structure with space group I4/mmm, according to the X-ray diffraction analysis. The pure phase of the sample was successfully synthesized using conventional solid-state reaction routes. The impedance spectroscopy was used to measure the electrical properties of the samples over a wide temperature range from 30 °C to 300 °C. At much higher temperatures, both samples showed an incomplete semicircle arc with the smallest resistance value. The samples prepared using conventional solid-state reaction routes exhibits higher conductivity as the sample has denser microstructure.

Abstract: Li₇La₃ZrSnO₁₂ was successfully prepared by conventional solid-state synthesis. Diffraction data show that the prepared sample has a mixture of two different phases. Both phases have tetragonal crystal symmetry but two different space groups, which are I41/acd and I4/mmm. Rietveld refinements were performed by using the models of the initial structures based on Li₇La₃Zr₂O₁₂ (I41/acdz) and Li₇La₃Ce₂O₁₂ (I4/mmm). It used to quantify the ratio between those two phases by employing Relative Intensity Ratio (RIR) technique. Crystal structure analysis showed that atomic arrangement in Li₇La₃Zr₂O₁₂ (I41/acdz) has more connected 3D tunnel for Li ions migration compared to Li₇La₃Ce₂O₁₂ (I4/mmm) that only connected tunnel at the edge of unit cell. Therefore, the existence of tetragonal phase with the space group of I4/mmm may resulting low ionic conductivity of Li ions at room temperature.

Abstract: A single-phase of Li₇La₃Ce₂O₁₂ samples that formed garnet-type crystal structure were prepared using the conventional solid-state method. Li₇La₃Ce₂O₁₂ formed a tetragonal garnet-type structure with the space group of I4/mmm. Impedance spectroscopy data show that Li₇La₃Ce₂O₁₂ can be classified as the ionic conductor as it has a mixture of ionic and electronic conductivities. Their electrical conductivities also obey Jonscher universal power law.

Abstract: High purity Li₇La₃Zr_1.0Sn_1.0O₁₂ samples that formed garnet-type crystal structure were prepared using biopolymer sol-gel method. The structure phase analysis of Li₇La₃Zr_1.0Sn_1.0O₁₂ powder was determined by using X-ray Diffraction (XRD). Impedance spectroscopy analysis was used to determine the electrical properties of Li₇La₃Zr_1.0Sn_1.0O_12. The electrical properties of the sample was observed from conductivity and resistance plots. The heterogeneity of sample was observed from Z’ and M” spectroscopic plot.

Abstract: High purity of Li₇La₃Zr_2-xSn_xO₁₂ (x = 0.00, 0.50, 1.00, 1.50 and 1.00) samples that formed garnet-type crystal structure were prepared using biopolymer sol-gel method. The structure phase of Li₇La₃Zr_2-xSn_xO₁₂ (x = 0.00, 0.50, 1.00, 1.50 and 1.00) powder was indexed with the parent composition of Li₇La₃Zr₂O₁₂ structure with space group of Ia-3d for cubic phase. Impedance spectroscopy analysis was used to determine the conductivity of Li₇La₃Zr_2-xSn_xO₁₂ (x = 0.00, 0.50, 1.00, 1.50 and 1.00) samples. The samples exhibit the conductivity about 10^-6 to 10^-4 Scm^-1 .The SEM micrographs reveal that the grain of the samples exhibits well developed particles of irregular shape.

Abstract: The BaTi_0.905Sn_0.095O₃ ceramic has been synthesized by using a solid-state method and sintered at 1450 °C in air for 3 hours. The doping effect of 9.5 mol% Sn into BaTiO₃ ceramic towards its crystal structure, dielectric properties and microstructure were investigated. The X-ray diffraction (XRD) analysis shows that the sample exhibited tetragonal structure with space group p4mm. The dielectric constant, ε_r measurement revealed that the sample reached the maximum ε_r value about 4393 when measured at T_c around 45 °C with frequency 1 kHz. The dielectric loss value was considerably low about below than 0.3 for the temperature range from 30 °C to 150 °C measured at 1 kHz. The capacitance value range lies between 10^-9 and 10^-10 indicates the bulk effect has dominated the electrical properties of the sample. It shows a good correlation with the microstructure results where the grains were well developed and homogenously distributed.

Abstract: The 5 mol% Fe-doped BaTiO₃ ceramic has been synthesized by using solid-state method. The sample was characterized by X-ray diffraction (XRD) and Impedance spectroscopy. It is interesting to note that the sample can developed a phase transformation between 1000 °C to 1350 °C. The XRD results showed that sample exhibited cubic structure when heated at 1000 °C and developed oxygen non-stoichiometry when it was heated at 1350 °C for 8 hours. It was confirmed by the ceramic color changes. The dielectric properties of the sample is relatively low which is due to the oxygen non-stoichiometry effect and gives the dielectric constant, ε_r value around 150 at 30 °C with frequency 1 kHz. The capacitance value of this sample lies within 10^-8 to 10^-10 which represents that the electrical properties of the sample has shown bulk and grain boundary response. There are pores that can be observed from the SEM images indicates the porosity of the sample which is in a good agreement with the low dielectric constant value. Moreover, the grains are composed of rectangular orientations, hexagonal shapes and inhomogeneous microstructures that might represent the coexistence of tetragonal and hexagonal phase of the sample.

Abstract: The dielectric properties and crystal structure of Ba_0.85Sr_0.15TiO₃ and Ba_0.85Sr_0.15Ti_0.92Zr_0.08O₃ ceramics were studied. The samples were synthesized by using solid-state method. The results show that the samples were single phase. The Ba_0.85Sr_0.15TiO₃ exhibited tetragonal structure (space group P4mm), while with addition of 8 mol% Zr into Ba_0.85Sr_0.15TiO₃ it shows that the sample exhibited orthorhombic structure (space group Amm2). The dielectric constant value increased from 1094 for pure, up to 4211 for Ba_0.85Sr_0.15Ti_0.92Zr_0.08O₃ ceramic at T_c measured at 1 kHz. The T_c decreased from 80 °C down to 60 °C as 8 mol% Zr ions doped into Ba_0.85Sr_0.15TiO₃ composition. The Ba_0.85Sr_0.15Ti_0.92Zr_0.08O₃ ceramic exhibited lower dielectric loss, tan δ about 0.006 compared to Ba_0.85Sr_0.15TiO₃ ceramic (tan δ = 0.009) when measured at 110 °C with frequency 1 kHz. The slope at low frequency region in capacitance vs frequency plot for both samples attributed by the grain boundary effect, whereas the high frequency plateau associated with the bulk response. The impedance spectroscopy analysis results show that both samples are dominated by the bulk response when an incomplete semicircle arc was observed in Zʺ vs Zʹ plot.