The formation of solid solutions of microwave dielectric compounds having compositions in the vicinity of Ba3.75-R 9.5Ti18O54 and/or BaO·R 2O3·4TiO2 (R=rare earth) has been investigated. 3BaO·2R 2O3·9TiO2 (Ba6 R 8Ti18O54) solid solutions with the ideal formulae of Ba6-3x R 8+2x Ti18O54 (0.0≤x≤1.0) have been derived on the tie line with the ratio Ti:O=1:3 between perovskite and R 2Ti3O9 based on the new tungsten bronze-type crystal structure with 2×2 perovskitelike unit cells. The type of solid solutions is substitutional with following the relation 3Ba2+\rightleftarrows2R 3++\Box. Lattice parameters as a function of composition have been determined by the WPPD (whole-powder-pattern decomposition) method.17) The formation range is located at 0.3≤x≤0.7 compositions in the case of R=Sm and 0.0≤x≤0.7 in R=Nd. In the latter case, two kinds of substitutions of the solid solutions are considered.

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Microwave ceramic resonators composed of BaO-Ti02-W0, were developed. The effect of WO, addition on the system of BaO*xTi02-(l +x)yWO, (x=4 and 4.5, y =O to 0.04) was studied. The ceramics of this system are composed of crystallines including Ba2Ti9020, BaTi40p, BaW04, and TiO?. At y=0.02, the Ba0.4Ti02* 0. I W03 ceramic was found to have excellent microwave properties such as E =35, Q=84OO at 6 GHz, and nearly 0 ppm/"C of rp T IS well-known that such BaTi409 and I B a T' iyOzo ceramics as compounds of the Ti02-rich region in BaO-Ti02 systems have good microwave properties, with a high dielectric constant ( F ) in the range of 35 to 40. However, for improved use as m i c r o w a v e r e s o n a t o r s , t h e h i g htemperature coefficient of resonant frequency ( T~) of BaTi4OY ceramics (8 =38, Q=9000 at 4 GHz) should be lowered to nearly zero from a high value (15 to 20 ppm/"C)." On the other hand, the Q of B a 2 T i y O z o ceramics ( E = 3 9 to 40, q = 2 ~pm/"C)'-~ should be increased to more than Q =8000 to 11000 at 4 GHz.In our study, it was found that small amounts of WO, added to the composition of Ba0.(4-4.5)TiO2 ceramics, equivalent to BaTi40y and BaZTi9OZo, has an explicit advantage for both decreasing the T~ of BaTi4OY ceramics and increasing the Q of Ba2Ti90zo ceramics. This paper is mainly concerned with the relation between the amount of WO,, microstructural observations, and the microwave properties of ceramics having a composition of Ba0.(4-4.5)TiOZ.(O-0 .22)W03. MATERIALS AND PROCEDUREThe starting materials composed of BaCO,, Ti02, and WO, powder with a purity of 99.7% to 99.9% were mixed to a designated composition of x =4 (BaTi409) to x=4.5 (Ba,Ti9O2") along with y=O to 0 . 0 4 in the formula B a 0 . x T i 0 2 . (1+x)yW03. The mixed powder was calcined at 1000°C in air for 4 h. Ball-milled powder was cold-pressed into disks and then sintered at 1360" to 1420°C in 0 2 for 2 h. The microwave properties were mea-CONTRIBUTING EDITOR-P. K. GALLAGHER

Dielectric crystals having composition in the vicinity of Ba3.75 R 9.5Ti18O54 and/or BaR 2Ti4O12 (R=La, Nd and Sm) were obtained from the melts with BaR 2Ti5O14 composition. A superlattice with two times the fundamental lattice spacing along the c-axis has been found in the three kinds of crystals. Crystal data of the superlattice are as follows: orthorhombic, P b n21 (No. 33) or P b n m (No. 62); a=12.267(5), b=22.410(9), c=7.732(6) Å for Ba3.75La9.5Ti18O54; a=12.189(3), b=22.319(6), c=7.677(4) Å for Ba3.75Nd9.5Ti18O54; a=12.142(4), b=22.300(6), c=7.653(4) Å for Ba3.75Sm9.5Ti18O54. Space group of the fundamental lattice is P b a2 (No. 32) or P b a m (No. 55). The dielectric constants, εr, of Ba3.75 R 9.5Ti18O54 (R=Nd and Sm) are in the high range from 78 to 86, and unloaded Q values are in the range of 2400 to 3000. The excellent values of single phase are better than those of BaR 2Ti5O14 composition including secondary phases.

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Ba6-3x (Sm1-y ,R y )8+2x Ti18O54 (R = Nd and La; x = 0.6, 0.0 ≤y ≤1.0) solid solutions in which Nd or La ions are substituted for Sm ions were studied from the point of microwave dielectric materials. In both Sm-Nd and Sm-La series, formation of solid solutions was found, which was deduced from linear change of the lattice parameters. We found high-quality resonator materials in the both series which show high ε r of 84, Q· f products of 9000 GHz, and temperature coefficient of resonance frequency τ f=0 ppm/\CC. The compositions of those materials in the Sm-Nd and the Sm-La series were determined to be y = 0.2 and 0.1, respectively. A relationship between dielectric constant and volume of octahedron is also stated.

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The microwave dielectric properties of the Ba6-3 x Sm8+2 x Ti18O54 (0.3≤x≤0.7) solid solutions are studied in relation to the crystal structure. Q·f of suitable materials obtained by optimizing the sintering condition is in inverse proportion to the dielectric constant (ε r ). With increase of x, ε r decreased and Q·f increased. Good-quality microwave resonators with ε r =80 and Q·f=9720 GHz can be obtained in the composition range of x=0.5 to 0.7 in the solid-solution region. Substitution of 2Sm3+ for 3Ba2+ in the large cation sites results in the creation of vacancies and crystal distortion, showing that the shrinkage of the TiO6 octahedral site plays an important role for improvement of the microwave dielectric properties.