Cubic phase stability, optical and magnetic properties of Cu-stabilized zirconia nanocrystals

Journal Article · 13 May 2018 · Journal of Physics. D, Applied Physics

DOI: https://doi.org/10.1088/1361-6463/aac004 · OSTI ID:1594022

Pramanik, Prativa  ^[1]; Singh, Sobhit  ^[2]; Joshi, Deep Chandra  ^[3]; Mallick, Ayan ^[3]; Pisane, Kelly ^[2]; Romero, Aldo H. ^[2]; Thota, Subhash  ^[3]; Seehra, M. S. ^[2]

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1. Indian Inst. of Technology (IIT), Assam (India); West Virginia University
2. West Virginia Univ., Morgantown, WV (United States)
3. Indian Inst. of Technology (IIT), Assam (India)

By means of experimental and ab initio investigations, in this article we report on the cubic phase stability of Cu doped zirconia (ZrO₂) at room temperature, and further characterize its structural, optical and magnetic properties. Various compositions of Zr_1–xCu_xO₂ (0.01 ≤ x ≤ 0.25) nanocrystallites of average size ~16 nm were synthesized using co-precipitation technique. Thermal analysis and kinetics of crystallization revealed that the cubic phase at ambient temperature can be stabilized by using a critical calcination temperature of 500 °C for 8 h in air and a critical composition of $$x_c$$ = 0.10 ± 0.05. For $$x < x_c$$, some undigested monoclinic phase of ZrO₂ exists together with the cubic structure. However, for $$x > x_c$$, the monoclinic CuO emerges as a secondary phase with shrinkage of unit-cell volume with increasing the Cu content. At x = 0.05 and 500 °C calcination temperature, we observe a high degree of cubic crystallinity which breaks down into monoclinic phase with increasing calcination temperature beyond 550 °C. Electron magnetic resonance studies provide evidence for the substitution of Cu²⁺ (²D_5/9,3d⁹) ions at Zr⁴⁺ sites with g_∥ = 2.250, g_⊥ = 2.018 and average g_a = (g_∥ + 2g_⊥)/3 ~ 2.1. The temperature dependence of magnetic susceptibility measurements from 2 K to 300 K exhibits Curie–Weiss behaviour whose analysis using g_a = 2.1 and spin S = 1/2 yields x = 0.028 and x = 0.068 for the nominal x = 0.05 and x = 0.20 samples, respectively. This magnetic analysis confirms the findings from x-ray diffraction that only a part of Cu is successfully doped into cubic phase of Cu-doped ZrO₂. The optical bandgap decreases with increasing x, which is due to the emergence of Cu-d states at Fermi-level near the valence bands, thus making Cu-doped zirconia a hole doped (p-type) semiconductor.

• Research Organization: West Virginia Univ., Morgantown, WV (United States)
• Sponsoring Organization: National Science Foundation (NSF); USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: SC0016176
• OSTI ID: 1594022
• Journal Information: Journal of Physics. D, Applied Physics, Journal Name: Journal of Physics. D, Applied Physics Journal Issue: 22 Vol. 51; ISSN 0022-3727
• Publisher: IOP PublishingCopyright Statement
• Country of Publication: United States
• Language: English