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Monolithic t‐ZrO2 (tetragonal structure) nanopowder is synthesized with an amorphous ZrO(OH)2·xH2O polymer precursor. The H2O molecules impart the structure and promote reconstructive thermal decomposition of the structure to t‐ZrO2 nanoparticles on heating at temperatures as low as 200°C. A prevalent endothermic heat output in the dissociation process controls the local temperature in exothermic nucleation and growth of various groups of the reaction species so that it is self‐controlled in high‐energy nanoparticles. Crystallites are, on average, d= 8 nm diameter, and they have a high value of Gibbs free energy or lattice volume Vo= 0.06770 nm3. The excess volume decreases to Vo= 0.06705 nm3 if the reaction temperature is increased to >200°C, i.e., approximately the bulk value of 0.06681 nm3; there is a minor increase to d= 12 nm at 600°C. Many oxygen vacancies in the thin surface space‐charge layers seem to support the stability of small particles in this particular polymorph. A pure m‐ZrO2 (monoclinic structure) appears with d= 22 nm at temperature as low as 800°C. The results are analyzed using X‐ray diffractometry, microstructure, infrared spectroscopy, and thermal studies of the polymer precursor and derivative t‐ZrO2 nanoparticles.

Mesoporous Sm(3+) doped CeO2 (Ce-Sm) with a nanocrystalline framework, a high content of Ce(3+) and surface area (184 m(2) g(-1)), have been synthesized through a facile aqueous solution-based surfactant assisted route by using inorganic precursors and sodium dodecyl sulphate as a template. The XRD results indicate that the calcined Ce-Sm and even the as-prepared material have a cubic fluorite structure of CeO2 with no crystalline impurity phase. XRD studies along with HRTEM results confirmed the formation of mesoporous nanocrystalline CeO2 at a lower temperature as low as 100 °C. A detailed analysis revealed that Sm(3+) doping in CeO2 has increased the lattice volume, surface area, mesopore volume and engineered the surface defects. Higher concentrations of Ce(3+) and oxygen vacancies of Ce-Sm resulted in lowering of the band gap. It is evident from the H2-TPR results that Sm(3+) doping in CeO2 strongly modified the reduction behavior of CeO2 by shifting the bulk reduction at a much lower temperature, indicating increased oxygen mobility in the sample which enables enhanced oxygen diffusion at lower temperatures, thus promoting reducibility, i.e., the process of Ce(4+)→ Ce(3+). UV-visible transmission studies revealed improved autocatalytic performance due to easier Ce(4+)/Ce(3+) recycling in the Sm(3+) doped CeO2 nanoparticles. From the in vitro cytotoxicity of both pure CeO2 and Sm(3+) doped CeO2 calcined at 500 °C in a concentration as high as 100 μg mL(-1) (even after 120 h) on MG-63 cells, no obvious decrease in cell viability is observed, confirming their excellent biocompatibility. The presence of an increased amount of surface hydroxyl groups, mesoporosity, and surface defects have contributed towards an improved autocatalytic activity of mesoporous Ce-Sm, which appear to be a potential candidate for biomedical (antioxidant) applications.

Mesoporous ZrO2 with a tetragonal (t) nanocrystalline framework was synthesized using zirconium propoxide as the zirconium precursor and cetyltrimethylammonium bromide as pore‐directing agent and subsequent calcination of the inorganic/organic intermediate. The Raman spectrum showed six distinct peaks at 146, 268, 325, 480, 615, and 645 cm−1, which further confirm t‐structure of the mesoporous ZrO2. Fourier transform infrared spectroscopy analysis reveals that mesoporous ZrO2 prepared at 500°C is template free. The mesoporous t‐ZrO2 possesses narrowly distributed pore size (2–11 nm) with average pore diameter of 5 nm and surface area of 65 m2/g. A photoluminescence band centered at 419 nm under excitation at 285 nm wavelength at room temperature is attributed to the ionized oxygen vacancy in t‐ZrO2 in the mesoporous structure. The combined effects of grain/pore size, oxygen vacancies and mesoporous wall strain–energy play important role in stabilizing the t‐nanocrystalline framework of mesoporous ZrO2. In comparison with the mesoporous ZrO2 materials stabilized by chemical treatment, the present route is simpler and resulted in mesoporous ZrO2 with crystalline framework.

Tetragonal (t) ZrO 2 nanoparticles have been obtained by a partial Eu 31 -Zr 41 substitution, synthesized using a simple oxalate method at a moderate temperature of 6501C in air. The Eu 31 additive, 2 mol% used according to the optimal photoluminescence (PL), gives small crystallites of the sample. On raising the temperature further, the average crystallite size D grows slowly from 16 nm to a value as big as 49 nm at 12001C. The Eu 31 :t-ZrO 2 nanoparticles have a wide PL spectrum at room temperature in the visible to near-IR regions (550-730 nm) in the 5 w