What is it about?

The development of a strategy to stabilise the cubic phase of HfO2 at lower temperatures is necessary for the emergence of unique properties that are not realised in the thermodynamically stable monoclinic phase. A very high temperature (>2600 °C) is required to produce the cubic phase of HfO2, whereas the monoclinic phase is stable at low temperature. Here, a novel rapid synthesis strategy was designed to develop highly crystalline, pure cubic-phase HfO2 nanoparticles (size <10 nm) using microwave irradiation. Furthermore, the as-prepared nanoparticles were converted to different morphologies (spherical nanoparticles and nanoplates) without compromising the cubic phase by employing a post-hydrothermal treatment in the presence of surface modifiers. The cytotoxicities and proliferative profiles of the synthesised cubic HfO2 nanostructures were investigated over the MCF-7 breast cancer cell line, along with caspase-3/7 activities. The low-temperature phase stabilisation was significantly attributed to surface imperfections (defects and deformations) induced in the crystal lattice by the desirable presence of Na2S·xH2O and NaOH. Our work provides unprecedented insight into the stabilisation of nanoscale cubic-phase HfO2 in ambient environments; the method could be extended to other challenging phases of nanomaterials.

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Why is it important?

To the best of our knowledge, this is the first report that presenting a novel solvent-free synthesis route for highly pure crystalline c-HfO2 nanoparticles (size <10 nm) in just a few minutes, by the reaction of HfCl4 with Na2S·xH2O under microwave heating. The obtained nanoparticles are further hydrothermally treated with different surface modifiers, such as PEG and FU to achieve nanostructured c-HfO2 of different morphologies and to study the cytotoxicity of the nanostructures towards MCF-7 breast cancer cells.


The coating of FU on c-HfO2 could augment the biological response of the cancer cells, consequently enhancing the efficacy of cancer therapies. The HfO2 nanostructures were relatively non-toxic to WS1 normal fibroblast cells. These findings offer a new rapid method to stabilise the cubic phase of HfO2 at low temperatures; this method could be expanded to realise the high-temperature phase stabilisation of other nanomaterials. This facile scalable synthesis of cubic HfO2 may also permit the examination of its new properties and the design of novel applications.

Dr Neeraj Kumar
Council for Scientific and Industrial Research

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This page is a summary of: A novel approach to low-temperature synthesis of cubic HfO2 nanostructures and their cytotoxicity, Scientific Reports, August 2017, Nature, DOI: 10.1038/s41598-017-07753-0.
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