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Solid Solution in LnTiO₂N and MTaO₂N Oxynitrides, Ln = La,Nd; M = Ca, Sr, Ba

J. Ahchawarattaworn, D.P. Thompson

Journal of Ceramic Science and Technology, Vol. 5, No. 3 (2014), pp. 173-183

DOI: 10.4416/JCST2014-00003

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Abstract

The last fifty years have witnessed a considerable level of interest in the field of oxynitrides. This has mainly been because of their thermal and mechanical properties, but certain members of this group have the perovskite atomic arrangement, and as such might be expected to have interesting electrical and electronic properties. Foremost among these are the rare earth titanium oxynitrides, LnTiO2N, with Ln = La and Nd the two rare earths most commonly investigated, and also the Group II tantalum oxynitrides of the type MTaO2N where M = Ca, Sr and Ba. The present paper explores the changes in structure which occur in solid solutions between end-members of these two series. In the (LapNd1-p)O2N series, the Pnma space group of the Nd end-member is retained up to p = 0.8 in the above formula; in the (BapSr1-p)TaO2N series, the cubic structure of BaTaO2N is retained up to p ∼ 0.5 before transforming into the tetragonal modification of SrTaO2N; in the (CapSr1-p)TaO2N series, the tetragonal structure of SrTaO2N is stable up to p ∼ 0.65 before changing into the orthorhombic form of CaTaO2N. No evidence was found for solid solutions between CaTaO2N and BaTaO2N.

Keywords

Oxynitrides, perovskites, synthesis, crystal structure, dielectric properties

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