International Journal of Inorganic Materials 1 (1999) 213–217 Low temperature dielectric properties of magnetoplumbite family of materials a a a a, b * Balaji Venkateshwaran , Manwen Yao , Ruyan Guo , Amar Bhalla , U. Balachandran a Materials Research Laboratory, The Pennsylvania State University, University Park, PA 16802, USA b Ceramic Section, Energy Technology Department Building, Argonne National Laboratory, Argonne, IL 60439, USA Received 16 April 1999; received in revised form 25 June 1999; accepted 15 July 1999 Abstract The magnetoplumbite family of materials exhibit properties that make them suitable to be used as substrates materials for microwave application. Four members of the family studied in this work are LaMgAI O , NdGaMgAl O , CaGa Al O and CaGa O . 11 19 10 19 6 6 19 12 19 Dielectric studies have been carried out over a temperature range of 4–300 K and a wide frequency range. All four exhibit a low dielectric constant with good temperature stability, low dielectric loss and favorable frequency dependence characteristics.  1999 Published by Elsevier Science Ltd. All rights reserved. Keywords: A. superconductors; A. oxides; A. magnetic materials; D. dielectric properties 1. Introduction twin-free growth of thin films on the substrates, chemical inertness and mechanical stability of the substrates. The With the advent of new superconducting oxide materi- aim of this investigation is to study four members of the als, the field of electronics has seen a great deal of magnetoplumbite family of materials over a wide tempera- potential in using this technology for a variety of applica- ture range, to assess the promise held by these materials as tions. Currently, there is an increasing interest in applying substrates for microwave applications [2]. thin film superconductors to a range of devices working at Most high speed microwave devices operate at low microwave and millimeter wave frequencies. The choice of temperatures as they use superconducting materials as a suitable substrate material for the growth of supercon- interconnects. In order to be used as substrates for micro- ducting thin films for various microwave applications is wave applications, the candidates need to possess a very critical for device performance. Also fine particles with low and temperature independent dielectric constant (ideal- suitable morphology and buffer layers of suitable orienta- ly), along with low tangent delta. The low dielectric tion of oxide materials are desirable for seeding grain constant is an important feature because device speeds oriented superconducting powder compacts, wire and tape drop as substrate dielectric constant increases and this for various applications. would defeat the purpose of using superconducting materi- Substrates for superconducting thin films for microwave als as high speed interconnects if the substrate material applications need to possess a range of characteristics in acts as a bottleneck. The four members of the magneto- order to be considered as potential candidates [1]. Depend- plumbite family that are studied in the present report are ing on the end use, a low / moderate dielectric constant, low LaMgAl O , NdGaMgAl O , CaGa O and 11 19 10 19 66 19 tangent delta, low temperature coefficient of dielectric CaGa O . 12 19 constant and intrinsic stability of dielectric constant over a Magnetoplumbites belong to one of the two typical given frequency range are a few key features of such types of hexaaluminates. These compounds have a layer substrate materials. Other factors include favorable lattice structure composed of spinel blocks and conduction layers matching between the substrate and superconductor, simi- which are stacked alternately [3]. A schematic of the larity in thermal expansion for good lattice matching, magnetoplumbite structure is shown in Fig. 1. In the magnetoplumbite compounds (AB O ), it is possible to 12 19 21 *Corresponding author. substitute the A ions with trivalent ions of about the 1466-6049 / 99 / $ – see front matter  1999 Published by Elsevier Science Ltd. All rights reserved. PII: S1466-6049(99)00033-1