Processing and microwave dielectric properties of barium magnesium tantalate ceramics for high-quality-factor personal c
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Processing and microwave dielectric properties of barium magnesium tantalate ceramics for high-quality-factor personal communication service filters Seung-Hyun Ra and Pradeep P. Phule´a) Department of Materials Science and Engineering, 848 Benedum Engineering Hall, University of Pittsburgh, Pittsburgh, Pennsylvania 15261 (Received 23 February 1999; accepted 19 August 1999)
A modified route, based on calcined MgO, Ta2O5, BaCO3, and ZrO2, was developed and used for preparation of barium magnesium tantalate (BMT) and barium zirconate (BZ)-doped BMT ceramics (BZ-BMT). The dielectric constant for BMT ceramics sintered at 1600 °C for 2 h was 24.9 at 7.28 GHz. The average long-range ordering parameter for undoped BMT ceramics was 0.81 ± 0.03 and the coresponding average quality factor and resonant frequench product (Qd ⭈ fo) was 147,000 ± 3800 GHz. A significant level of B-site long-range cation disorder was introduced as a result of BZ doping of BMT ceramics. The average ordering parameters for 3 and 4 mol% BZ-doped BMT were found to be 0.69 ± 0.06 and 0.49 ± 0.13, respectively. The decrease in ordering parameters did not lead to a dramatic decrease in the corresponding average quality factors of 3 mol% BZ-BMT (Qd ⭈ fo ⳱ 127,000 ± 3800 GHz) and 4 mol% BZ-BMT (Qd ⭈ fo ⳱ 139,000 ± 4200 GHz). The results suggest that the B-site cation ordering is not a primary factor that influences the observed microwave loss in BMT ceramics. The influence of atomic level point defects, induced from raw material impurities, processing, etc., may be more important in controlling the quality factor of BMT ceramics.
I. INTRODUCTION
The personal communication services (PCS) and other wireless technology industries, such as direct broadcasting, global positioning, and collision avoidance systems, have witnessed an explosive and an almost unprecedented growth in applications. High-frequency devices are now routinely used in mobile communication systems, satellite communication systems, wireless local area networks, and other systems.1–3 In this emerging and rapidly growing area research on new and improved devices and new materials and processing techniques will be important in catalyzing the continued growth of the aforementioned technologies. The architecture of many important microwave passive components for wireless applications utilizes a dielectric resonator (DR) as the building block. A DR is an unmetallized piece of a relatively high dielectric constant (k), low dielectric loss (i.e., high-quality factor Qd) material. In general, we refer to quality factors Q ⳱ fo/⌬f. The quality factor is approximately the inverse of the loss tangent (tan ␦), i.e., Q ∼ 1/tan ␦. Thus, high Q implies low loss and vice a)
Address all correspondence to this author. J. Mater. Res., Vol. 14, No. 11, Nov 1999
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versa. The subscript to Q refers to the source, i.e., d in Qd refers to the dielectric. Many practical resonators are a cylindrical rod or puck shape
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