Journal of Physics and Chemistry of Solids 69 (2008) 805–814 Phase composition-dependent physical and mechanical properties of Yb x Zr 1x O 2x/2 solid solutions M. Hartmanova´ a,Ã , F. Kubel b , V. Bursˇ ı´kova´ c , E.E. Lomonova d , J.P. Holgado e , V. Navra´til f , K. Navra´til g , F. Kundracik h a Institute of Physics, Slovak Academy of Sciences, 84511 Bratislava, Slovakia b Institute of Chemical Technologies and Analytics, Vienna University of Technology, A—1060 Vienna, Austria c Department of Physical Electronics, Faculty of Sciences, Masaryk University, 61137 Brno, Czech Republic d General Physics Institute, Russian Academy of Sciences, 119991 Moscow, Russia e Institute of Material Science, University of Sevilla—C.S.I.C., 41092 Sevilla, Spain f Department of Physics, Faculty of Education, Masaryk University, 60300 Brno, Czech Republic g Institute of Condensed Matter, Faculty of Sciences, Masaryk University, 61137 Brno, Czech Republic h Department of Experimental Physics, Faculty of Mathematics, Physics and Informatics, Comenius University, 84248 Bratislava, Slovakia Received 26 February 2007; received in revised form 3 September 2007; accepted 3 September 2007 Abstract The paper represents a detailed insight into the correlation between changes of the phase composition of crystalline Yb x Zr 1x O 2x/2 solid solutions and their structural, electrical, mechanical and optical properties. Particularly, the effect of the crystal growth conditions and stabilizer amount in the range of 1.5–13.8 mol% of Yb 2 O 3 are studied in terms of Rietveld analysis of powder X-ray diffraction data, electrical conductivity measured by impedance spectroscopy, absorption coefficient and refractive index measurements, Vickers microhardness (classical technique) as well as the plastic microhardness and effective elastic modulus (DSI—depth-sensing indentation technique). Potential applications of the investigated systems are discussed in view of the results obtained. r 2007 Elsevier Ltd. All rights reserved. Keywords: D. Electrical conductivity 1. Introduction Ytterbia-(like Sm-) stabilized zirconia (YbSZ) is a mixed conductor with the ionic and electronic conductivities above 800 1C [1,2]. Therefore, this system is not very suitable for high-temperature applications, such as tradi- tional solid oxide fuel cells (SOFC). Regardless of this problem, high operating temperatures always result in high fabrication costs and accelerate the degradation of the fuel cell system. Therefore, current activities in the SOFC materials research are increasingly focused on lowering operating temperatures from usual values of E1000 to 500–800 1C. There are several methods how to improve the efficiency and to reduce operating temperatures of the SOFC. One approach is to use alternative ionic conductors with a higher ionic conductivity than YSZ, usually used as the electrolyte in the SOFC. Another possibility is to use a thin film electrolyte to minimize ohmic losses resulting in a higher power density [3]. Therefore, just ytterbia stabilized zirconia (YbSZ), which belongs to the solid oxides with the fluorite (F)-type structure and essentially ionic electrical conductivity below 600 1C [2], could be a suitable candidate. Stabilized zirconias posses also good mechanical and optical properties, such as high hardness [4,5] and a relatively high refractive index [6,7]. Therefore, in addition to the SOFC, they are usually promising candidates for other bulk/thin film applications, such as protective coat- ings on metals, in planar SOFCs, etc. [8,9]. The purpose of the present study was to obtain a more complete insight into electrical, mechanical and optical properties of Yb 2 O 3 -stabilized zirconia systems as ARTICLE IN PRESS www.elsevier.com/locate/jpcs 0022-3697/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2007.09.002 Ã Corresponding author. Tel.: +421 2 59410545; fax: +421 2 5477 6085. E-mail address: maria.hartmanova@savba.sk (M. Hartmanova´).