A New BaO‐TiO₂ Compound with Temperature‐Stable High Permittivity and Low Microwave Loss

Abstract

The dielectric properties of ceramics in the Ti0,-rich region of the BaO-TiO, system were investigated. In the composition range between BaTi,O, and TiO,, another compound, Ba,Ti,O,,, can be obtained when calcining and sintering conditions are controlled carefully. When dense and single-phase, this ceramic has excellent dielectric and physical properties. At 4 GHz, the dielectric K = 39.8, Q = 8000, and T~ (tern erature coefficient of dielectric constant) = -2 4 k 2 p p m k I . Introduction IELECTRIC microwave resonators offer the possibility of D high-quality integrated filters. The primary obstacle to the study and application of filters utilizing dielectric resonators has been the lack of a suitable material. A dielectric resonator is a piece of unmetalized ceramic with a high dielectric constant in which the electromagnetic fields are confined to the dielectric region and its immediate vicinity by reflections at the dielectric-air interface. The dielectric properties required for practical microwave filters are high dielectric Q (>3000) and a low temperature coefficient of dielectric constant (~~= O f 4 0 ppm/"C). In addition, a high dielectric constant (K>35 to 40) is desirable.The Ti-rich region of the BaO-TiO, system has seemed promising for locating a composition which exhibits temperature compensation while retaining suitable K and loss properties. Several compositions with temperature-independent dielectric constants at radio frequencies have been reported. Bunting and co-workers,',* who surveyed the dielectric properties of the Ba0-Sr0-Ti0, system at 1 MHz, observed temperature compensation with low loss and K = 37 for the binary composition containing 83.3 mol% TiO,. In a study of the ternary systems BaO-SnO,-TiO, and BaO-ZrO,-TiO,, Jonker and KwestrooJ found a promising combination of dielectric properties at 1 MHz for ternary compositions containing 18.5 mol% BaO and =4mol% SnO, or ZrO,. On theother hand, Schwarzbach and Plocek4 reported temperature compensation in the binary at 80 mol% TiO, (BaTi,O,) and an increasingly negative7 as the amount of BaO was decreased. The work of Naumann et u L .~ agrees well with Ref. 4. There has been less investigation at microwave frequencies. Masse and c o -~o r k e r s~~~ reported that temperature compensation is best for BaTi,O,, for which K=39, Q=2500, and ~~= -4 9 X 10-fi/cC. Table I summarizes the results of these studies for the 75 to 100 mol% TiO, region of the BaO-TiO, system.The data on phase relations in this system are also confusing. In an apparently thorough investigation, Rase and RoyR found only 3 binary compounds, BaTi,O,, BaTi,O,, and TiO,, for the region 75 to 100 mo19 TiO,. On the other hand, Jonker and Kwestroo? using similar experimental conditions, identified Ba2Ti90,, within the Ti0,-rich binary region. Schwarzbach and Plocek4 also reported the existence of a Ba,Ti,O,, phase in the binary system, but their structure data did not agree with those of Jonker and Kwestroo. T i l l m a n n~~~'~ has reported the existence of BaTi,Ol, and BaTi,O,...

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