Low loss dielectric ceramics for microwave applications: a review

S. Bindra Narang,Shalini Bahel 한양대학교 세라믹연구소 2010 Journal of Ceramic Processing Research Vol.11 No.3

Microwave dielectric ceramics have been used for a wide range of applications from wireless communication (including mobile communication, ultra high speed local area networks, intelligent transport system, satellite communication) to consumer electronic products. The need for portable, light weight and multifunctional electronic components has forced scientists to search for new advanced microwave materials. During the past 25 years, a large number of dielectric materials have been developed and the properties of existing materials have been improved. However, the data on these very useful materials are scattered. The main purpose of this review is to bring together the data of low loss microwave dielectric ceramics and classify them according to their applications. This should be of immense help to researchers and technologists all over the world.

High Frequency Dielectric Behavior of Rare Earth Substituted Sr-M Hexaferrite

S. Bindra Narang,Anterpreet Singh,Kulwant Singh 한양대학교 세라믹연구소 2007 Journal of Ceramic Processing Research Vol.8 No.5

Strontium hexaferrites of a structural formula Sr1-xRExFe12O19, where RE=La3+, Nd3+ and Sm3+ with (x=0 to 0.30) were prepared by a standard ceramic technique. The lattice constants, density, porosity, dielectric constant and dielectric loss tangent were studied on a series of rare earth substituted strontium hexaferrites. The dielectric constant and dielectric loss tangent were measured in the frequency range of 0.3 GHz to 3.0 GHz at room temperature. The dielectric constant decreased with increasing frequency for all the three series. This behavior of dielectric properties with frequency has been explained with the Maxwell-Wagner type interfacial polarization in agreement with the Koops phenomenological theory. The substitution of rare earth ions into SrFe12O19 increases the value of the dielectric constant. This increase in dielectric constant could be due to the electronic exchange between Fe2+ ↔ Fe3+ and results in a local displacement determining the polarization of the ferrites. For these ferrite samples the Curie temperature decreases as rare earth ions substitution increases. Strontium hexaferrites of a structural formula Sr1-xRExFe12O19, where RE=La3+, Nd3+ and Sm3+ with (x=0 to 0.30) were prepared by a standard ceramic technique. The lattice constants, density, porosity, dielectric constant and dielectric loss tangent were studied on a series of rare earth substituted strontium hexaferrites. The dielectric constant and dielectric loss tangent were measured in the frequency range of 0.3 GHz to 3.0 GHz at room temperature. The dielectric constant decreased with increasing frequency for all the three series. This behavior of dielectric properties with frequency has been explained with the Maxwell-Wagner type interfacial polarization in agreement with the Koops phenomenological theory. The substitution of rare earth ions into SrFe12O19 increases the value of the dielectric constant. This increase in dielectric constant could be due to the electronic exchange between Fe2+ ↔ Fe3+ and results in a local displacement determining the polarization of the ferrites. For these ferrite samples the Curie temperature decreases as rare earth ions substitution increases.

Synthesis and microwave characterization of Bi- substituted barium lanthanum titanate

S. Bindra Narang,Shalini Bahel,Dalveer Kaur 한양대학교 세라믹연구소 2007 Journal of Ceramic Processing Research Vol.8 No.5

Bi-substituted barium lanthanum titanates with the general formula Ba4(La(1-z)Biz)9.33Ti18O54 where z = 0.0 to 0.2 in steps of 0.05 were synthesized by a conventional mixed oxide route. The composition and morphology were determined using scanning electron microscopy (SEM) and X-ray powder diffraction analysis (XRD). Two dielectric performance parameters, namely dielectric constant and loss tangent were measured with varying microwave frequency in the range 0.3 to 3 GHz at room temperature. It was observed that the dielectric constant and loss tangent both increased initially for z ≤ 0.10 and then decreased. The best properties were obtained for z = 0.20 with a dielectric constant of 91.4 and loss tangent of 0.004. This could be a promising microwave material with a high dielectric constant and low loss. Bi-substituted barium lanthanum titanates with the general formula Ba4(La(1-z)Biz)9.33Ti18O54 where z = 0.0 to 0.2 in steps of 0.05 were synthesized by a conventional mixed oxide route. The composition and morphology were determined using scanning electron microscopy (SEM) and X-ray powder diffraction analysis (XRD). Two dielectric performance parameters, namely dielectric constant and loss tangent were measured with varying microwave frequency in the range 0.3 to 3 GHz at room temperature. It was observed that the dielectric constant and loss tangent both increased initially for z ≤ 0.10 and then decreased. The best properties were obtained for z = 0.20 with a dielectric constant of 91.4 and loss tangent of 0.004. This could be a promising microwave material with a high dielectric constant and low loss.

Structural and microwave dielectric properties of Ba6-3xGd8+2xTi18O54 solid-solutions

S.Bindra Narang,Dalveer Kaur,Kulwant Singh Thind 한양대학교 세라믹연구소 2009 Journal of Ceramic Processing Research Vol.10 No.5

Ba6-3xGd8+2xTi18O54 (x = 0.0, 0.2 ≤ x ≤ 0.7) composites have been synthesized by employing a solid-state reactive sintering technique and studied from the point of view of microwave dielectric materials. In this series, formation of solid solutions was found, which was deduced from the linear change of the lattice parameters of the unit cells. Unit-cell parameters (Å) have been obtained with the help of the X-Ray powder diffraction (XRD) technique. Multi-phase microstructures have been observed for all the compositions using Scanning electron microscopy (SEM). We found good quality microwave materials which show a high dielectric constant (ε') of 70 and a low loss tangent (tanδ) of 0.006336 at 3 GHz. A minimum value of the A.C. dielectric conductivity (σa.c.) was 2.32E-12 mho/cm at 0.8 GHz. Ba6-3xGd8+2xTi18O54 (x = 0.0, 0.2 ≤ x ≤ 0.7) composites have been synthesized by employing a solid-state reactive sintering technique and studied from the point of view of microwave dielectric materials. In this series, formation of solid solutions was found, which was deduced from the linear change of the lattice parameters of the unit cells. Unit-cell parameters (Å) have been obtained with the help of the X-Ray powder diffraction (XRD) technique. Multi-phase microstructures have been observed for all the compositions using Scanning electron microscopy (SEM). We found good quality microwave materials which show a high dielectric constant (ε') of 70 and a low loss tangent (tanδ) of 0.006336 at 3 GHz. A minimum value of the A.C. dielectric conductivity (σa.c.) was 2.32E-12 mho/cm at 0.8 GHz.

Microwave dielectric properties of M-Type barium, calcium and strontium hexaferrite substituted with Co and Ti

Sukhleen Bindra Narang,I.S. Hudiara 한양대학교 세라믹연구소 2006 Journal of Ceramic Processing Research Vol.7 No.2

Suitable ferrite components are designed for use in systems like radar, satellite uplinks, industrial heaters or dryers and nuclear systems which employ high power microwaves. Ferrites are also used as microwave absorbers. Radar absorbing paint made from ferrites can be used to coat military aircraft for stealth operation. In this study, some hexaferrites have been synthesized and characterized for their possible use at high frequencies. Three series of M type hexagonal ferrites having the general formula MeFe12O19 in which Me was Ba2+, Sr2+ or Ca2+ and Fe3+ ions were replaced partly by Co2+Ti4+ ions were chosen for synthesis and study. The microwave dielectric constants of these hexaferrites has been measured in the X band of the microwave frequency range after successively increasing the amount of substituted ions in the ferrites. The variation of Complex Permittivity of these hexaferrites with change in composition as well as change in frequency has been measured in this frequency range. Important inferences have been drawn using theoretical concepts.

Processing, dielectric behavior and conductivity of some complex tungsten-bronze dielectric ceramics

Sukhleen Bindra Narang,Dalveer Kaur,Kulwant S. Thind 한양대학교 세라믹연구소 2006 Journal of Ceramic Processing Research Vol.7 No.1

Ceramic samples of a complex structural formula Ba6-3xR8+2xTi18O54, where R is a rare-earth oxide and R=Sm, Nd and Gd and x=0.2-0.7 were prepared by a high temperature solid-state reaction technique. The dielectric properties (i.e. dielectric constant (ε'), dielectric loss (ε'') and Q-factor) have been measured on the sintered disks with respect to the frequency in the range 0.3 GHz-3.0 GHz at room temperature. The dielectric properties of the synthesized samples have been found out to be a function of the wt.% of rare-earth oxides used. Dielectric conductivity (σ) was derived from the dielectric constant and loss tangent data in the same frequency range. Conductivity calculations were carried out based on this derived formula. The capacitance values have been calculated knowing the geometrical dimensions of the samples synthesized.

Electrical and magnetic properties of rare earth substituted strontium hexaferrites

Anterpreet Singh,S. Bindra Narang,Kulwant Singh Thind,O.P. Pandey,R.K. Kotnala 한양대학교 세라믹연구소 2010 Journal of Ceramic Processing Research Vol.11 No.2

Samples of strontium ferrite (Sr-M) with different molar substitution concentrations of lanthanum, neodymium and samarium ions were prepared by a standard ceramic processing technique. AC conductivity, dielectric constant and dielectric loss tangent measurements were carried out in the frequency range of 20 Hz to 1MHz. The experimental results indicate that AC electrical conductivity increases with increasing frequency. The increase in AC conductivity with frequency can be explained on the basis of Koops model, whereas the dielectric constant and dielectric loss tangent variations have been explained with a Maxwell-Wagner type interfacial polarization in agreement with the Koops phenomenological theory. The effects of rare earth substitution on the magnetic properties such as the saturation magnetization moment (Ms), coercive field (Hc), remenance (Mr),and Curie temperature Tc (K) have been investigated. It is found that the values of the magnetization moment (Ms), and remenance (Mr) decrease with increasing rare earth ions substitution for all the series. The reason for the decrease may be both the magnetic dilution and spin canting, which promote reduction of superexchange interactions. The enhancement of Hc values may be due to higher magnetocrystalline anisotropy, where Fe2+ ion anisotropy on the 2a site could be dominant in all hexaferrites series.