Crystal Structure and Microwave Dielectric Properties of LiRE9(SiO4)6O2 Ceramics (RE = La, Pr, Nd, Sm, Eu, Gd, and Er). Issue 5 (1st March 2013)

• Record Type: Journal Article
• Authors: Manu, Kurusaroor Mana; Karthik, Chinnathambi; Leu, Lii‐Cherng; Lazar, Kokken Anlin; Ubic, Rick; Sebastian, Mailadil Thomas; Tan, X.
• Is Part Of: Journal of the American Ceramic Society. Volume 96:Issue 5(2013)
• Page Start: 1504
• Page End: 1511
• Publication Date: 2013-03-01
• Subjects: Ceramics -- Periodicals; 620.1405
• DOI: 10.1111/jace.12215
• Languages: English
• ISSNs: 0002-7820

Abstract

<abstract abstract-type="main" id="jace12215-abs-0001"> <title> <x xml:space="preserve">Abstract</x> </title> <p>The crystal structure and microwave dielectric properties of apatite‐type LiRE<sub>9</sub>(SiO<sub>4</sub>)<sub>6</sub>O<sub>2</sub> ceramics (RE = La, Pr, Nd, Sm, Eu, Gd, and Er) have been investigated. The densification of lithium apatites has been greatly improved with the addition of 1 wt% LiF. Selected area electron diffraction and X‐ray diffraction (XRD) Rietveld analysis confirm that these compounds belong to the <italic>P</italic>6<sub>3</sub>/<italic>m</italic> (No. 176) space group with hexagonal crystal symmetry. The porosity‐corrected relative permittivity was found to decrease with decreasing ionic polarizability of RE<sup>3+</sup> ions. Relationships between the structural parameters and microwave dielectric properties have been examined. The observed variation in the quality factor of LiRE<sub>9</sub>(SiO<sub>4</sub>)<sub>6</sub>O<sub>2</sub> + 1 wt% LiF ceramics (RE = La, Pr, and Nd) was correlated with average cation covalency (%). The temperature coefficient of resonant frequency was found to depend on the bond valence sum of cations. LiEr<sub>9</sub>(SiO<sub>4</sub>)<sub>6</sub>O<sub>2</sub> + 1 wt% LiF ceramics showed good microwave dielectric properties with ε<sub>r</sub> = 12.8, <italic>Q</italic><sub>u</sub> × <italic>f</italic> = 13000 GHz and τ<sub>f</sub> = +17 ppm/°C. All the compositions showed low coefficient of thermal expansion with thermal conductivity in the range 1.3–2.8 W (m K)<sup>−1</sup>.</p> </abstract>