Abstract
Phononic excitations have been investigated using Raman scattering studies on CaCu3Ti4O12 and SrCu3Ti4O12 compounds as a function of temperature down to 10 K. Evidence of the Fano resonance effect is found in the Ag(1) mode with an asymmetric phonon line shape that occurs because of composite electron–phonon scattering due to the onset of metallic fractions in the system. The evolution of the Fano line shape with temperature affirms the existence of nanoscale phase separation and the prominence of orbitally disrupted metallic regions above 100 K. Anomalies in the evolution of the line width of the Ag(1) Raman mode with temperature are observed around 100 K where these compounds show an orbital order/disorder transition. These anomalies manifest mutual coupling of orbital degrees of freedom to lattice degrees of freedom.
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