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Báo cáo hóa học: " Scanning Probe Microscopy on heterogeneous CaCu3Ti4O12 thin films"

Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Scanning Probe Microscopy on heterogeneous CaCu3Ti4O12 thin films | Fiorenza et al. Nanoscale Research Letters 2011 6 118 http www.nanoscalereslett.eom content 6 1 118 o Nanoscale Research Letters a SpringerOpen Journal NANO EXPRESS Open Access Scanning Probe Microscopy on heterogeneous CaCu3Ti4O12 thin films Patrick Fiorenza Raffaella Lo Nigro Vito Raineri Abstract The conductive atomic force microscopy provided a local characterization of the dielectric heterogeneities in CaCu3Ti4O12 CCTO thin films deposited by MOCVD on IrO2 bottom electrode. In particular both techniques have been employed to clarify the role of the inter- and sub-granular features in terms of conductive and insulating regions. The microstructure and the dielectric properties of CCTO thin films have been studied and the evidence of internal barriers in CCTO thin films has been provided. The role of internal barriers and the possible explanation for the extrinsic origin of the giant dielectric response in CCTO has been evaluated. I. Introduction The electrical properties of CaCu3Ti4O12 CCTO ceramics and single crystals received considerable attention due to the effective huge permittivity up to 105 measured in the radio frequencies range furthermore stable in the 100-400 K temperature range 1-3 . In the recent literature this giant permittivity has been commonly related to extrinsic effects i.e. not associated to the bulk material property itself. Possible extrinsic mechanisms to account for the colossal permittivity behaviour have been supported by results from impedance spectroscopy IS 4 Raman spectroscopy 5 and first-principles calculations 6 . In particular the IS data on CCTO polycrystalline ceramics reported so far have been modelled considering an equivalent circuit of two elements each consisting of a parallel resistor-capacitor RC connected in series. One RC element Rgb and Cgb simulates the grain boundary response whereas the other Rb and Cb simulates the bulk contribution 4 . The model is suitable to simulate in a first approximation the measured .