Synthesis of shape-controlled ferromagnetic CrO2 nanoparticles by reaction in micelles of Cr6+–PVA polymer chelates

A chemical reaction of CrO3 with polymer molecules of poly vinyl alcohol (PVA) and sucrose in water is explored to synthesize CrO2 (D4h14:P42/mnm tetragonal crystal structure) of shape-controlled ferromagnetic particles. Under hot conditions, small species of Cr6+–PVA polymer chelates react in divided groups in micelles, resulting in a Cr4+–polymer complex, which retains in isolated groups of micelles dispersed in the water. When heating (after aging and drying), the polymer burns out at 300–400 °C in air, leaving behind a pure CrO2 of prismatic or ellipsoidal shape. Average diameter varies in such particles from 50 to 300 nm depending on the final temperature.