S. Bindra Narang

Dielectric Anomaly in La Modified Barium Titanates

In this study, we report on the frequency dependence of dielectric and conductivity properties of a Ba6 - 3xLa8 + 2xTi18O54 compound with x = 0.6 in a temperature range of 283–523 K. X-Ray diffraction confirmed the formation of single-phase compound in the orthorhombic system. Dielectric constant was observed to be decreased with increase in frequency. A dielectric anomaly has occurred at 323 K. Dielectric constant was constantly higher up to certain temperature, but then decreased linearly with rise in temperature. Loss tangent was observed to increase with temperature and frequency. A.C. conductivity increased with temperature and was frequency independent at higher frequencies.

DIELECTRIC INVESTIGATIONS OF LANTHANIDES (Ln = Sm, Nd AND Gd) SUBSTITUTED BARIUM TITANATE MICROWAVE CERAMICS

ABSTRACT Dielectric properties have been investigated and compared for three series of ceramic compounds based on complex oxides with molecular formula Ba6 − 3x Ln8 + 2x Ti18O54 with Ln (lanthanide) = Sm, Nd and Gd and x = 0.0 – 0.7. X-Ray diffraction (XRD) was employed to study the crystal structure of the sintered ceramics. Fired densities have been observed to be almost constant up to a certain composition then decreased with an increase in x. Values of dielectric constant (ϵ′) and loss tangent (tanδ) were decreased with increased composition as well as frequency. The temperature coefficient of resonant frequency (τf) was estimated in the temperature range of 20°C to 80°C.

Structural and Dielectric Properties of Ca Doped Barium Iron Niobate

Ceramic materials with high dielectric constant are being used in many electric and electro-optics applications. Ca substituted barium iron niobate with general formula (Ba1-xCax) (Fe0.5Nb0.5)O3 with x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 were prepared by conventional solid state reaction method. Structural properties were investigated using X-ray diffraction and scanning electron microscope. Two types of phases were observed for 0.4 ≤ x ≤ 08. Dielectric constant and loss tangent were measured using impedance analyzer in the frequency range of 20 Hz–1 MHz at room temperature. Dielectric constant and loss tangent were found to decrease with increasing the frequency. A relatively good combination of dielectric constant and loss tangent was obtained for x = 0.2 (ϵr = 1441 and tan δ = 0.19) at 10 KHz.

Electromagnetic properties of Co-Zr substituted Ba-Sr ferrite-paraffin wax composite for EMC/EMI applications

The electromagnetic parameters of synthesized M-type hexagonal ferrite composites, Ba<inf>0.5</inf>Sr<inf>0.5</inf>Co<inf>x</inf>Zr<inf>x</inf>Fe<inf>(12–2x)</inf>O<inf>19</inf> (x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0), are measured from 0.1–18 GHz. The ferrite composites exhibit dielectric behavior contrary to conventional magnetic nature of ferrite composites. The electron hopping between Fe²⁺ ions and Fe³⁺ ions enhances dielectric properties making it useful for EMI/EMC applications. The relationship is established between microstructure and microwave properties. The damped domain wall dispersion is observed along low frequency region. The various mechanisms behind variations of investigated parameters are discussed.

Investigation of microwave and electrical characteristics of Co–Zr substituted M-type Ba–Sr hexagonal ferrite

Abstract Microwave characteristics of M-type hexagonal ferrite, Ba0.5Sr0.5CoxZrxFe(12-2x)O19 (x = 0.0 to 1.0 in steps of 0.2), have been investigated as a function of frequency and substitution at X-band. The microwave absorption has been investigated using absorber testing device method. The static I-V characteristics have been studied as a function of substitution. The results show maximum microwave absorption at higher substitution. The static current exhibits ohmic behavior from 0 to 3 V and exponential trend from 3 to 4.8 V. The microstructure influences both microwave and electrical properties. The ferrite compositions for different electromagnetic applications are also suggested by measuring the microwave absorbed, transmitted and reflected power.

Temperature Dependent Dielectric Behavior of Neodymium Substituted Barium Titanate Ceramics

We report the investigations on the temperature dependent dielectric properties of Nd substituted Barium titanate compounds with compositional formula Ba6–3xNd8+2xTi18O54 (x = 0.0, 0.3 and 0.6) in a wide temperature range of −160°C to +160°C, at selected frequencies (10 KHz, 50 KHz, 100 KHz, 500 KHz, 1 MHz). Variation of dielectric parameters (i.e. dielectric constant and loss tangent) with respect to temperature showed an anomaly that occurred at low temperatures for the three compounds that were synthesized. The temperature range in which the anomalies were observed was found to be −70°C to −90°C. The temperature of the anomaly shifted to lower temperature with an increase in composition. Temperature coefficient of resonant frequency was estimated to be +92.2878 ppm/°C.

Investigation of microwave characteristics of Ca-Co-Ti ferrite for electromagnetic applications

In this investigation, we are reporting microwave characterization of M-type CaCo x Ti x Fe (12−2x) O 19 ferrite for different electromagnetic applications using Absorber Testing Device (ATD) [1] method.

Microwave absorption studies of M-type Ba 0.5 Sr 0.5 Co x Ti x Fe (12−2x) O 19 ferrite and its dependence on static properties

Microwave absorption, of M-type hexagonal Ba_0.5Sr_0.5Co_xTi_xFe_(12-2x)O₁₉, ferrite was studied as a function of thickness, frequency and substitution at X-band. Hysteresis measurements have been carried using vibrating sample galvanometer. Sample 1.0 with RL of 21 dB has potential for absorber and EMC/EMI applications.

TEMPERATURE DEPENDENT DIELECTRIC PROPERTIES OF Ba-La-Sm-Bi-Ti-O CERAMIC SYSTEM

ABSTRACT The temperature dependent dielectric properties of some of the compounds in Ba-La-Sm-Bi-Ti-O ceramic system have been studied for developing temperature stable high dielectric constant ceramics. Two series, Ba4(La0.5-zSm0.5Biz)9.33Ti18O54, and Ba4(La0.3-zSm0.7Biz)9.33Ti18O54, where z = 0.0, 0.1, 0.2, have been synthesized by conventional mixed oxide route and characterized. The study revealed that the substitution of rare earths (Sm, La) and Bi has been found effective in achieving high dielectric constant along with stabilizing the variation in dielectric constant with temperature. Ba4(La0.5-zSm0.5Biz)9.33Ti18O54 with z = 0.2 and Ba4(La0.3-zSm0.7Biz)9.33Ti18O54 with z = 0.1 posses high dielectric constant with small temperature variation of the resonant frequency (± 5 ppm/°C). These could be dielectric materials for practical applications.

Effects of Temperature Variation on Dielectric Properties of Ba4(La(1 - z)Biz)9.33Ti18O54 Solid Solutions

Bi modified Ba4La9.33Ti18O54 solid solutions were synthesized by conventional mixed oxide route. The three composition with molar formula Ba4(La(1 - z)Biz)9.33Ti18O54 where z = 0.0, 0.1 and 0.2 were characterized for structural and dielectric properties. A detailed study related to variation in dielectric properties namely dielectric constant and dielectric loss with change in temperature from 298 K to 423 K was carried out in the frequency range 10 kHz–10 MHz. It was observed that dielectric constant decreases as the temperature increase from 298 K to 423 K in the entire frequency range for all the three samples. There was very small change in dielectric loss. The temperature coefficient of resonant frequency was estimated to improve from 273.8 ppm/K to 54.5 ppm/K as Bi contents increases from z = 0.0 to 0.2. Such materials would be a suitable candidate for applications in mobile communications.