Temperature-stable, medium-permittivity dielectric ceramics have been used as resonators in filters for microwave (MW) communications for several decades. The growth of the mobile phone market in the 1990s led to extensive research and development in this area. The main driving forces were the greater utilization of available bandwidth, that necessitates extremely low dielectric loss (high-quality factor), an increase in permittivity so that smaller components could be fabricated, and, as ever in the commercial world, cost reduction. Over the last decade, a clear picture has emerged of the principal factors, that influence MW properties. This article reviews these basic principles and gives examples of where they have been used to control microwave properties and ultimately develop new materials.

Microwave Dielectric Ceramics for Resonators and Filters in Mobile Phone Networks

Since 1970s, many kinds of dielectric resonator materials with improved Q values and improved temperature coefficients have been developed. Representative of them are the systems, (Ba, Sr, Ca)(Zr, Ti)O3, MgTiO3-CaTiO3-La2O3 · TiO2, Ba2Ti9O20, (Zr, Sn)TiO4, (Sr, Ca)[(Li, Nb),Ti]O3, and BaO-Nd2O3-TiO2. In the past 15 years, the Q values of these materials have gradually been improved. Using these new materials, dielectric resonator filters and oscillators are being developed which are more compact and applicable to high power operation. Their main applications are cellular mobile radio systems and SHF-TV systems using direct broadcasting satellite. This paper will present the recent development in Japan of resonator materials and filters.

Recent development of dielectric resonator materials and filters in Japan

A method of preparing particles of a drug substance or diagnostic imaging agent which comprises grinding the drug substance or imaging agent in the presence of grinding media comprising a polymeric resin. The method provides particles exhibiting reduced contamination.

Method of grinding pharmaceutical substances

Small substitutions of BaZrO 3 into Ba[(Zn,Ni) 1/3 Ta 2/3 ]O 3 are utilized in the commercial preparation of low-loss perovskite microwave dielectrics. The structures of a series of these phases with substitution levels ranging from 1% to 5% BaZrO 3 were examined using high-resolution TEM. For < 2.15% BaZrO 3 the solid solutions retain the ordered 1:2 structure of the Ba[(Zn,Ni) 1/3 Ta 2/3 ]O 3 end-member but are comprised of small ordered domains whose size decreases as the Zr content is raised. The decrease in the size of the domains parallels a decrease in the processing time required to access a low-loss state. Although for pure Ba[(Zn,Ni) 1/3 Ta 2/3 ]O 3 reductions in the degree of cation order produce a large increase in the dielectric loss, the Zr-substituted ceramics retain a very low loss. We believe the low losses of the 1:2 ceramics are derived from the stabilization of the ordering-induced domain boundaries via the partial segregation of the Zr cations. For substitutions between 3% and 5% BaZrO 3 the size of the ordered domains continues to decrease but the system undergoes an abrupt transformation to a cubic 1:1 ordered structure with a doubled perovskite repeat. The structures of these phases have been interpreted using a random layer model in which one site is occupied by Ta and the other by a random distribution of Zn, Zr, and the remaining Ta cations, i.e., Ba{[Zn (2-y)/3 Ta (1-2y)/3 Zr y ] 1/2 [Ta 1/2 ]}O 3 . Although the ordering is confined to nano-sized domains, these ceramics also exhibit low losses, again reflecting the relative stability of the domain boundaries. In this case we believe the low losses reflect the effectiveness of the random layer in stabilizing the anti-phase boundaries.

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Effect of Ordering‐Induced Domain Boundaries on Low‐Loss Ba(Zn1/3Ta2/3)O3‐BaZrO3 Perovskite Microwave Dielectrics

CHAPTER 7 – SOLID SOLUTIONS OF Pb(Ti, Zr, Sn, Hf)O3

The dielectric properties at microwave frequencies of Ba(Zn1/3Ta2/3)O3 ceramics prepared by sintering were investigated. These ceramics had lower density but higher loss quality than ceramics hot-pressed at 1400°C. Loss quality was greatly improved by prolonged sintering. The Q of the ceramics measured by the dielectric resonator method was 14 000 at 12 GHz. The ceramics were investigated by X-ray diffraction analysis. It was found that Q improvement corresponds with increased Zn and Ta ordered structures in the ceramics.

Ba(Zn1/3Ta2/3)O3 Ceramics with Low Dielectric Loss at Microwave Frequencies

Ceramic compositions within the polygonal area defined by the formulas Pb(Mn1/3Ta2/3)0.030Ti0.470Zr0.500O3 Pb(Mn1/3Ta2/3)0.250Ti0.500Zr0.250O3 Pb(Mn1/3Ta2/3)0.375Ti0.375Zr0.250O3 Pb(Mn1/3Ta2/3)0.250Ti0.125Zr0.62503 ARE PARTICULARLY USEFUL FOR MAKING TRANSDUCER ELEMENTS.

Piezoelectric ceramic compositions

Effects of additives on the piezoelectric properties of Pb(Mg1/3Nb2/3)O3-PbTiO3-PbZrO3 ceramics in a perovskite-type structure are described. The tetragonality of Pb(Mg1/3Nb2/3)0.375-Ti0.375Zr0.25O3 ceramics increased with the addition of NiO, Cr2O3, or Fe2O3 but decreased with the addition of MnO2 or CoO. The dielectric and piezoelectric properties of the base composition were improved markedly through selection of additives in proper amounts. Addition of NiO yielded a high dielectric constant and planar coupling coefficient for compositions at the morphotropic transition boundary. High mechanical Q-factors and low electrical dissipation factors were obtained by addition of MnO2. Addition of both NiO and MnO2 produced a mechanical Q-factor of 2051 and a planar coupling coefficient of 0.553. The resonant frequency of Pb(Mg1/2Nb2/3)0.4375Ti0.4375 zr0.125O3 containing MnO2 had very low temperature and time dependence. The microstructure indicated that ceramics with a high mechanical Q-factor had a fine, uniform grain structure. Addition of Cr2O3 retarded grain growth and addition of MnO2, NiO, CoO, or Fe2O3 promoted grain growth in the ternary system.

Piezoelectric Properties of Pb(Mg1/3Nb2/3)O3 PbTiO3 -PbZrO3 Ceramics Modified with Certain Additives

Provided is a method for milling ceramic powder which comprises wet-milling at least one ceramic powder by a media agitating mill wherein the volume of liquid is 4 times or less the net-volume of the ceramic powder. A dispersing agent is added and milling is carried out using grinding media of 1 mm, or less, in diameter. Further, a media agitating mill used for the above method is provided which comprises a milling chamber, grinding media and an agitator wherein the peripheral speed of the agitator is 10 m/s or more, the grinding media have a diameter of 1 mm or less and packing fraction of the grinding media is 65-85 vol %. A method for making a sintered body from fine powder produced by the above milling method is also disclosed.

Media agitating mill and method for milling ceramic powder

In an agitating mill for producing the objective fine powder, the agitating medium having an average particle diameter of no more than 0.6mm is charged in an annular gap (3) between the external side wall of the agitator (2) and the internal side wall of the milling vessel (1). Thereby the agitator (2) can be rotated at a peripheral speed of no less than 30m/s, and it results in a high grinding rate and reduced amount of impurity which means worn-out grinding media included in the objective fine powder.

Nishida Masamitsu

Papers

Ba(Zn1/3Ta2/3)O3 Ceramics with Low Dielectric Loss at Microwave Frequencies

Piezoelectric ceramic compositions

Piezoelectric Properties of Pb(Mg1/3Nb2/3)O3 PbTiO3 -PbZrO3 Ceramics Modified with Certain Additives

Media agitating mill and method for milling ceramic powder

Agitating mill and method for milling