Surface morphology and dielectric properties of alkoxy-derived Sr2Ta2O7 and Sr2Ta, Nb2O7 thin films

Sr₂Ta₂O₇ and Sr₂(Ta, Nb)₂O₇ thin films were prepared from molecular structure-controled alkoxide solutions. The Sr₂Ta₂O₇ thin films initiated to crystallize at around 650 °C and showed random orientation. The surface topography developed was dependent on the solutions. In the thin films prepared from the ethanolic solution, grains formed at low temperatures. However, many small pores still remained and no grains were observed in the thin films prepared from the methoxyethanolic solution. In contrast, the 800 °C-annealed Sr₂(Ta, Nb)₂O₇ thin films showed the (0 k 0) orientation as in Sr₂Nb₂O₇ thin films. The dielectric constants and loss factors of the 750 °C-annealed Sr₂Ta₂O₇ and Sr₂(Ta_0.7Nb_0.3)₂O₇ thin films were around 90 and less than 0.05 at 100 kHz, respectively.     

Effect of Zr+4 ion substitution on the structural, dielectric and electrical properties of Sr5LaTi3Nb7O30 ceramics

Polycrystalline Zr-modified Sr₅LaTi₃Nb₇O₃₀ compound was prepared by a high-temperature solid-state reaction technique. X-ray structural analysis confirmed the formation of compound in an orthorhombic system at room temperature. Detailed studies of the dielectric parameters (dielectric constant and tangent loss) as a function of frequency (1–100 kHz) at different temperature (150 to 650 K) were carried out. It was found that as Zr⁺⁴ concentration increases in Sr₅LaTi_{3 – x} ZrxNb₇O₃₀, the value of dielectric constant decreases. These compounds show ferroelectric-paraelectric phase transition of diffuse type at 283, 305 and 320 K for x = 0, 1 and 2 respectively. The transition temperature (T _c) shifts towards higher temperature and maximum dielectric constant value (_max) decreases with increasing Zr⁺⁴ concentration for x = 0 to x = 2. When Ti⁺⁴ cations were completely replaced by Zr⁺⁴ cations (i.e., Sr₅LaZr₃Nb₇O₃₀), the compound does not show any phase transition. Impedance-spectroscopic studies provided an insight into the electrical properties and understanding of relaxation behavior of the material. Measurement of electrical conductivity as a function of temperature suggests that the compounds have a negative temperature coefficient of resistivity (NTCR) with a typical semiconductor behavior.     

Dielectric properties of BaBi2Nb2O9 ceramics

The crystal structure and dielectric properties as a function of temperature for Ba-based with Bi-layered structure BaBi₂Nb₂O₉ (BBN) ceramics were investigated. The obtained results confirmed the relaxor ferroelectric behavior of the studied ceramics, including a strong frequency dispersion of the permittivity maximum and a visible shift of its temperature with frequency. Analysis of the real and imaginary part of permittivity allowed us to determine the values of Burn’s temperature and of the freezing temperature characterizing the relaxor ferroelectrics. The physical processes, responsible for the relaxor behavior of the studied ceramics are discussed. The additional low frequency dielectric dispersion at high temperatures in the paraelectric phase range was also observed. Correlation between this dispersion and the thermally stimulated depolarization current was ascertained.     

Densification and anisotropic grain growth in Sr2Nb2O7

Sr : Nb stoichiometry and donor-doping with La were found to affect densification behavior and anisotropic grain growth in Sr₂Nb₂O₇ ceramics. La-doping improved the high temperature a.c. resistivity, but inhibits grain growth by grain boundary pinning. The presence of excess Nb was found to promote anisotropic grain growth by forming a liquid at the grain boundaries in both undoped and doped Sr₂Nb₂O₇. Anisotropic grain growth in La-doped Sr₂Nb₂O₇ can be controlled by incorporating large template particles in a Nb-rich matrix. High sintered densities (98% of theoretical) were achieved in both undoped and La-doped samples.     

Dielectric and impedance properties of Ba2Sr3DyTi3V7O30 ceramics

A new member of tungsten bronze family, Ba₂Sr₃DyTi₃V₇O₃₀, was synthesized by a high-temperature solid-state reaction method. Studies of structural by X ray diffraction technique and micro-structural by scanning electron microscope brings out orthorhombic crystal structure and densely packed nonuniform grains for the above ceramic system. Detailed dielectric studies as a function of temperature (30–500?°C) at different frequencies (1–1,000?kHz) reveals diffuse-phase-transition and loss anomaly at 81?°C. Detailed studies of impedance parameters provide a better understanding of the electrical properties and type of relaxation processes in the material. Temperature variation of dc and ac conductivity shows that this compound exhibits negative temperature coefficient of resistance. The frequency variation of ac conductivity shows that the compound obeys Jonscher’s universal power law.     

Ferroelectric,dielectric and piezoelectric properties of Sr0.6(BiNa)0.2Bi2Nb2O9 ceramics

Aurivillius-type ceramic, Sr_0.6(BiNa)_0.2Bi₂Nb₂O₉ (SBNBN), was synthesized by using conventional solid-state processing. Phase structure and microstructural morphology were confirmed by X-ray diffraction analyses (XRD) and the scanning electron microscopy (SEM). Dielectric, piezoelectric and electromechanical properties of the SBNBN ceramic were investigated in detail. Curie temperature (T_c), piezoelectric coefficient (d₃₃), electromechanical coupling coefficient k_p, k_t and quality factor Q_m of the SBNBN ceramic were found to be 586.5 °C, 22 pC/N, 5.0%, 8.7% and 651, respectively. In addition, the reasons for varieties of the resistivity and dielectric properties at high temperature were also discussed.     

Synthesis and electrical properties of Sr4Mn2CuO9 ceramics

The crystal structure of the compound Sr₄Mn₂CuO₉ is closely related to the hexagonal perovskite structure. In this work, Sr_3.95Mn₂CuO₉ was synthesized by solid state methods and the electrical properties of the polycrystalline ceramics were measured. The conductivity was observed to increase four orders of magnitude over the temperature range 100 to 700 K, with a room temperature conductivity of 5×10⁻⁵ S/cm. The conductivity closely followed an Arrhenius equation with an activation energy of approximately 0.14 eV.     

Dielectric and impedance properties of LiCa2Nb5O15 ceramics

Polycrystalline sample of LiCa₂Nb₅O₁₅ was prepared by a high-temperature solid-state reaction technique. Structural and microstructural characterizations were performed by X-ray diffraction (XRD) and scanning electron microscope (SEM). X-ray studies reveal that the material has orthorhombic structure at room temperature. Electrical properties of the material have been studied using a complex impedance spectroscopy (CIS) technique in a wide temperature (31–500 °C) and frequency (10²–10⁶ Hz) ranges. The complex impedance plots reveal the main contribution of bulk effects in it. The bulk resistance, evaluated from complex impedance spectrum, has been observed to decrease with rise in temperature showing a typical negative temperature coefficient of resistance (NTCR) behavior. Variation of dc conductivity (bulk) with temperature demonstrates that the compound exhibits Arrhenius type of electrical conductivity.     

Dielectric properties of Sr3CuNb2O9 perovskite ceramics

The dielectric constant ? and loss tangent tanδ of Sr₃CuNb₂O₉ perovskite ceramics prepared by solid-state reactions have been measured at temperatures from 300 to 900 K and frequencies from 25 to 1 × 10⁶ Hz. The results demonstrate that the samples slowly cooled from the temperature of the final, high-temperature firing (1200°C) have relatively low permittivity (? ? 10) and dielectric losses (tanδ ? 0.005 at 1 kHz) at room temperature, with no strong dielectric dispersion and no prominent maxima in the temperature dependences of their permittivity and dielectric loss. The ceramics quenched from 1300°C exhibit a pronounced Debye-type low-frequency relaxation and strong dielectric dispersion in conjunction with high permittivity ? ? 2000 at low frequencies and/or high temperatures. The observed dielectric anomalies in the Sr₃CuNb₂O₉ ceramics can be understood in terms of Maxwell-Wagner relaxation at dielectric inhomogeneities associated with the quenching-induced difference in oxygen-vacancy concentration between the grain bulk and surface layer.     

Study on low temperature sintering and electrical properties of CuO-doped Ca0.28Ba0.72Nb2O6 ceramics

Ca_0.28Ba_0.72Nb₂O₆ (CBN28) ceramics with different content of CuO were prepared by the conventional ceramic fabrication technique. The effects of CuO content on the phase structure, microstructure, dielectric and ferroelectric properties of obtained CBN28 ceramics were investigated. XRD results showed that pure tungsten bronze structure was obtained in all ceramics and CuO additive could accelerate the phase formation at lower temperatures. The CuO aid was effective for the uniform grain size in CBN28 ceramics, as it could facilitate the sintering behavior and suppress the anisotropic growth behavior obviously. The dielectric and ferroelectric properties of CBN28 ceramics depended greatly on the CuO content. Curie temperature T _c and dielectric loss tanδ both shifted downward, whereas the maximum dielectric constant ε _m and the dielectric constant around room temperature ε _r all increased initially and then decreased as x increased from 0.1 to 0.4 wt%. Normal ferroelectric hysteresis loops could be observed in all compositions, and the remnant polarization P _r decreased gradually. It was found that the comprehensive electric performance was optimized in CBN28-0.2 wt% CuO ceramics: ε _r = 453, ε _m = 3,371, T _c = 226 °C, tanδ = 0.048, P _r = 4.72 μC/cm² and E _c = 13.81 kV/cm, showed that CuO sintering aid could not only ameliorate the sintering behavior but also improve the electrical properties.     

Liquid phase sintering of Re2O3 YSZ ceramics: Part II Grain boundary electrical properties

Grain boundary electrical properties of Y₂O₃ stabilised zirconia with small additions of Er₂O₃ and Pr₂O₃ sintered via silicate liquid phase were studied by the impedance spectroscopy technique. Grain boundary specific conductivity of the praseodymium doped samples was found to be independent of sintering time, while the erbium doped sample showed high anomalous conductivity for the 1.0 h sintered samples. The electrical behaviour is explained considering the grain boundary to be a series association of the glass film and the space charge region. Specific conductivity and Debye length of the space charge region of erbium doped samples were found to be 6.7 × 10^–8 S/cm and 0.25 nm, respectively.     

Microstructure and electrical properties of Nb2O5 doped titanium dioxide

The present work attempts to investigate the sintering characteristics, grain boundary morphology and electric conductivity of Nb₂O₅ doped TiO₂ semiconductor ceramics. X-ray diffraction results showed evidence of a second phase beside the rutile TiO₂ when Nb₂O₅ exceeds 0.7 mol%. SEM images showed that Nb₂O₅ doping can lowers the sintering temperature of TiO₂, although not significantly. Lattice images of the grain boundary morphology obtained by high resolution transmission electron microscopy revealed defects introduced from the doping. Grain boundaries vary from amorphous to a faceted structure. Finally, electrical conductivity measurements showed that the grain boundary resistance is greatly reduced at high temperature.     

Microwave dielectric properties of Sr2Ce2Ti5O16 ceramics

Sr₂Ce₂Ti₅O₁₆ dielectric ceramics were prepared by conventional solid-state ceramic route. The structure and microstructure of the ceramics were investigated by X-ray diffraction and scanning electron microscopic methods. The Sr₂Ce₂Ti₅O₁₆ has a psuedocubic structure. It has ɛ_r of 113, unloaded quality factor (Q_u × f) of 8000 GHz and temperature coefficient of resonant frequency of 306 ppm/°C. The effects of various dopants on the structure, microstructure and microwave dielectric properties of the material have been investigated. It is found that addition of small amount of dopants such as PbO, Al₂O₃, Nd₂O₃, MoO₃, CeO₂, La₂O₃, Fe₂O₃ and NiO improve the microwave dielectric properties of Sr₂Ce₂Ti₅O₁₆.     

Effect of Co3+ on structure and electrical properties of Na0.5Bi2.5Nb2O9 ceramics

Journal of Materials Science: Materials in Electronics - Na0.5Bi2.5Nb2-xCoxO9 (NBNC-x, x?=?0.00, 0.02, 0.05, 0.07, 0.09) bismuth layered piezoelectric ceramics were synthesized by the...     

Dielectric, magnetic and electrical properties of ZnFe2O4 ceramics

The polycrystalline sample of ZnFe₂O₄ was prepared by a high-temperature solid-state reaction technique. Preliminary X-ray diffraction studies of the compound showed the formation of a single-phase compound at room temperature. Studies of dielectric properties (ε_r, tan δ) of the above compound as a function of frequency in a wide temperature range show dielectric anomalies signifying existence of possible ferroelectric to paraelectric phase transition in the material. The confirmation of this assumption was made with observation of ferroelectric hysteresis loop at room temperature. Magnetic measurement exhibits anti-ferromagnetic nature of the sample. Studies of the zero-field cooled and the field-cooled magnetization in dc field provided the blocking temperature T_B. The temperature dependence of electrical parameters (impedance, modulus, conductivity, etc.) of the material exhibits a strong correlation between the microstructure (i.e., bulk, grain boundary, etc.) and electrical parameters of the material. Detailed studies of impedance parameters have provided an insight into the electrical properties and understanding of types of relaxation process in the material. The temperature variation of dc resistivity/conductivity exhibits negative temperature coefficient of resistance behaviour of the material. The frequency dependence of ac conductivity suggests that the material obeys Jonscher’s universal power law.