ORIGINAL PAPER Fe 3 O 4 stabilized zirconia: structural, mechanical and optical properties M. Bashir • S. Riaz • S. Naseem Received: 31 January 2014 / Accepted: 27 May 2014 Ó Springer Science+Business Media New York 2014 Abstract Zirconia (ZrO 2 ) is one of the most well studied transition-metal oxides in the optical and biological fields. The applications area of ZrO 2 can be increased by addition of metal oxides. Aim of this study is to determine the effect of acidic and basic Fe 3 O 4 nanoparticles’ (NPs) doping in sol–gel synthesized ZrO 2 . Different samples are prepared by varying Fe 3 O 4 concentrations, acidic and basic, in the range of 2–10 wt%. Sols of Fe 3 O 4 doped ZrO 2 (FOZ) are spin coated onto glass substrates at 3000 rpm for 30 s. FOZ films are annealed at 300 °C for 1 h. It is worth mentioning that Fe 3 O 4 nanoparticles (acidic and basic) are used for the first time, to the best of our knowledge, to stabilize zirconia using sol–gel technique. Moreover, completely homoge- nous FOZ sol is obtained using water as a solvent. X-ray diffraction results confirm the formation of phase pure tetragonal ZrO 2 (t-ZrO 2 ) along with less intense peak of Fe 3 O 4 at 8–10 wt% of basic dopant. Optical spectra reveal that energy band gap lies in the range of 4.8 to 5.0 eV whereas, high value of transmission up to 80 % has been observed in case of basic dopant. Refractive indices vary with the variation in crystal structure and density of the films. Redshift is observed in Fe 3 O 4 doped zirconia. Hardness of the samples is in the range of 310 to 962 HV. Keywords ZrO 2  Thin films  Fe 3 O 4  Tetragonal  Mechanical 1 Introduction Preparation and characterization of zirconia thin films are of major interest due to their excellent optical and mechanical properties. These films can be employed in optical and biomedical fields including broadband interference filters, active electro-optical devices, luminescent oxygen sensors, buffer layers for growing superconductors, biomedical and prosthetic coatings, and protective coatings on devices working in high temperature environments [1–5]. Zirconium dioxide (ZrO 2 , zirconia) has exceptional crystallographic phases that greatly improves its strength and toughness [6]. Zirconia crystals can have a monoclinic (m), tetragonal (t) or cubic (c) structures which are ther- modynamically stable. Monoclinic phase (m-phase) is sta- ble at temperatures below 1100 °C, tetragonal structure (t- phase) is stable in the temperature range of 1100–2370 °C, and cubic structure (c-phase) is stable above 2370 °C[7]. The formation of crystal structure is due to arrangements and spacing of atoms (zirconium and oxygen) [8, 9]. Zir- conia displays useful physical and chemical properties for example thermal and chemical stability, high strength and fracture toughness, low thermal conductivity, high corro- sion resistance along with acidic and basic nature [10]. The transformable tetragonal zirconia is used as engineering ceramic material since it shows high values of strength and hardness. It is used as a dental structural material for mul- tiple unit posterior bridges [11]. Occurrence of multi phases of zirconia results in cracks which consequently degrades the mechanical and optical properties due to scattering and interference phenomenon [4, 12]. Therefore, it is mandatory to obtain a single phase. Among all phases tetragonal has been considered as a strong and osseoconductive ceramic, hence suitable for high strength and stress bearing appli- cations [13]. However, as mentioned earlier tetragonal M. Bashir (&)  S. Riaz  S. Naseem Centre of Excellence in Solid State Physics, University of the Punjab, QAC, Lahore 54590, Pakistan e-mail: mahwish_shaikh20@yahoo.com 123 J Sol-Gel Sci Technol DOI 10.1007/s10971-014-3415-4