Effect of Ca2+ Substitution on the Structure, Microstructure, and Microwave Dielectric Properties of Sr2Al2SiO7 Ceramic. Issue 12 (15th October 2013)

• Record Type: Journal Article
• Authors: Manu, Kurusaroor Mana; Karthik, Chinnathambi; Ubic, Rick; Sebastian, Mailadil Thomas; Chen, X. M.
• Is Part Of: Journal of the American Ceramic Society. Volume 96:Issue 12(2013)
• Page Start: 3842
• Page End: 3848
• Publication Date: 2013-10-15
• Subjects: Ceramics -- Periodicals; 620.1405
• DOI: 10.1111/jace.12598
• Languages: English
• ISSNs: 0002-7820

Abstract

<abstract abstract-type="main" id="jace12598-abs-0001"> <title> <x xml:space="preserve">Abstract</x> </title> <p>The effect of Ca<sup>2+</sup> substitution on the structure, microstructure, and microwave dielectric properties of Sr–gehlenite (Sr<sub>2</sub>Al<sub>2</sub>SiO<sub>7</sub>) ceramic has been investigated. The structure and microstructure of Sr<sub>2−<italic>x</italic></sub>Ca<sub><italic>x</italic></sub>Al<sub>2</sub>SiO<sub>7</sub> ceramics were analyzed via X‐ray diffraction (XRD) as well as scanning and transmission electron microscopic techniques. While the end‐members (<italic>x</italic> = 0 and 2) form isostructural compounds, a highly defective, nonstoichiometric, Ca‐rich secondary phase was observed via bright‐field transmission electron microscopy and energy dispersive X‐ray spectroscopy in compositions corresponding to <italic>x</italic> = 0.75 and 1.5. The concentration of secondary phase in <italic>x</italic> = 0.75 is too low to be detected via XRD or scanning electron microscopy. Identical selected‐area electron‐diffraction patterns of the compounds (<italic>x</italic> = 0, 1, and 2) confirmed that they belong to the space group <italic>P</italic><alternatives><inline-graphic mimetype="image" xlink:href="ark:/27927/pgg3zmnbf6g" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><mml:math altimg="urn:x-wiley:00027820:media:jace12598:jace12598-math-0001" overflow="scroll" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mrow><mml:mn>4</mml:mn></mml:mrow><mml:mrow><mml:mo stretchy="false">¯</mml:mo></mml:mrow></mml:mover></mml:math></alternatives>2<sub>1</sub><italic>m</italic> (no. 113) with tetragonal crystal symmetry. The porosity‐corrected relative permittivity at microwave frequencies showed a gradual increase with Ca<sup>2+</sup> content; however, Ca<sup>2+</sup> substitution made only marginal changes to the microwave dielectric properties except in the case of <italic>x</italic> = 1.5, in which the secondary phase reduced the quality factor considerably. Thermal conductivity decreased with increasing Ca<sup>2+</sup> content, and the compounds with defective structures showed the lowest thermal conductivity. All the compounds exhibited low coefficients of linear thermal expansion, with values varying in the range 2.3–3.6 ppm/°C.</p> </abstract>