Cover Picture: Observation of insulating–insulating monoclinic structural transition in macro-sized VO2 single crystals (Phys. Status Solidi RRL 3/2011)



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To clarify the origin of metal–insulator transition (MIT) in VO2, it is of crucial importance to under-stand the interplay among monoclinic M1, monoclinic M2, and rutile R phases. The Letter by Bongjin Simon Mun et al. (pp. 107–109) reports the unusual insula-tor–insulator structural phase transition (SPT) of VO2 single crystals, which involves monoclinic M1 and M2 phase. The VO2 crystals exhibit an extremely abrupt MIT at 67.8 °C and an insulator–insulator transition (IIT) at ∼49 °C. Using synchrotron-based X-ray microdiffraction, it is found that the IIT in this VO2 crystal is related to a SPT between the M2 and M1 phases while the MIT occurs with a SPT of M1 and R phase. Also, a stable M2 phase is found at room temperature without any presence of external stress, which has not been reported previously. The authors believe that further investigations on this intriguing system will not only enrich the fundamental understanding of the system, but also will be exploited in future technologies.