The effects of temperature and composition on the thermal conductivities of [(ZrO 2 ) 1x (CeO 2 ) x ] 0.92 (Y 2 O 3 ) 0.08 (0 6 x 6 1) solid solutions Fan Yang, Xiaofeng Zhao, Ping Xiao ⇑ Materials Science Centre, School of Materials, University of Manchester, Manchester M13 9PL, UK Received 18 April 2011; received in revised form 15 October 2011; accepted 16 October 2011 Available online 14 December 2011 Abstract The thermal conductivities of [(ZrO 2 ) 1x (CeO 2 ) x ] 0.92 (Y 2 O 3 ) 0.08 (0 6 x 6 1) solid solutions are studied in this paper. The incorporation of ZrO 2 and CeO 2 in the solid solution decreases the thermal conductivity compared with their end members (YSZ and YDC). The ther- mal conductivities of the solid solutions show clearly different temperature dependences in the ZrO 2 -rich (0 6 x 6 0.5) region and in the CeO 2 -rich region (0.5 6 x 6 1). The composition and the temperature dependence of the thermal conductivities are discussed based on established phonon scattering theories. We have concluded that the composition dependence of the thermal conductivity of this system is mainly controlled by the mass difference between Zr 4+ and Ce 4+ , while the thermal conductivity–temperature relationship is dominated by the randomness of the defect distribution. Ó 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Thermal conductivity; ZrO 2 –CeO 2 –Y 2 O 3 solid solutions; Mass disorder; Oxygen vacancy; Defect distribution 1. Introduction Zirconia-based ceramics are state of the art materials for thermal barrier coatings (TBC). Pure zirconia is not suit- able for such applications due to two main disadvantages. Firstly, the thermal conductivity of pure zirconia is not suf- ficiently low to fulfil the ideal thermal barrier function. Sec- ondly, its phase transformation from the high temperature tetragonal phase to the room temperature monoclinic phase involves volume expansion and leads to cracking and coating failure. These two disadvantages can be over- come by doping other metal oxides into zirconia. Numer- ous studies have found that dopants play an important role in both decreasing the thermal conductivity and stabi- lizing the high temperature tetragonal or cubic phases of zirconia [1]. The efficacy of a dopant in reducing the thermal conduc- tivity of zirconia is largely dependent on the valence of its metal cation. Sub-tetravalent oxides are the most effective dopants in decreasing the thermal conductivity as they lead to oxygen vacancy formation, which are generated to com- pensate for the missing charge arising from substitution of Zr 4+ by lower valency cations. Oxygen vacancies strongly scatter phonons and therefore decrease the thermal con- ductivity. For example, yttria-stabilized zirconia (YSZ), the currently predominant TBC material, shows an almost temperature-independent low thermal conductivity due to the high concentration of oxygen vacancies [2–4]. In the case of tetravalent oxides the substitution of Zr 4+ by a homovalent cation does not create any vacancies in the zir- conia lattice. In this case, the reduction in thermal conduc- tivity is attributed only to substitutional defects at the cation sites, which have been proven to be less effective than oxygen vacancies in decreasing the thermal conductiv- ity [1]. 1359-6454/$36.00 Ó 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.actamat.2011.10.030 ⇑ Corresponding author. Tel.: +44 161 3065941; fax: +44 161 3063586. E-mail address: ping.xiao@manchester.ac.uk (P. Xiao). www.elsevier.com/locate/actamat Available online at www.sciencedirect.com Acta Materialia 60 (2012) 914–922