Orbital molecule fluctuations in vanadate spinels
In certain materials, notably with the spinel structure, orbital ordering can result in the formation of a ground state with electrons delocalising between small numbers of adjacent cations, called ‘orbital molecules’. AlV2O4 is notable as it undergoes a long range structural and charge ordering transition to form V7 clusters, the largest known orbital molecules, below 700 K. We have recently synthesised a new analogue GaV2O4 which has the same rhombohedral spinel superstructure. Variable temperature PND study showed that long range orbital molecule order persists up to TCO = 470 K. Magnetic susceptibility data provide strong evidence that the V7 clusters persist above TCO where the average crystal structure is cubic spinel with no long range orbital molecule distortions, so the clusters must be present in a glassy or liquid-like disordered state. The high incoherent scattering cross-section of V, makes this material ideal for INS. QENS from IN6 will be particularly useful as it enables the V self-self correlation function to be extracted, giving the timescale for the cluster fluctuations and hence showing whether the high temperature state is an cluster liquid or glass.
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J. Paul Attfiel;d; BROWNE Alexander; Simon AJ Kimber; KOZA Michael Marek and Calum Lithgow. (2016). Orbital molecule fluctuations in vanadate spinels. Institut Laue-Langevin (ILL) doi:10.5291/ILL-DATA.7-01-450