Temperature dependent total scattering structural study of CaCu ₃Ti₄O₁₂

X-ray and neutron powder diffraction data as a function of temperature are analysed for the colossal dielectric constant material CaCu₃Ti ₄O₁₂. The local structure is studied using atomic pair distribution function analysis. No evidence is found for enlarged oxygen or Ti displacement parameters suggesting that short range octahedral tilt disorder and off-centre Ti displacements are minimal. However, an unusual temperature dependence for the atomic displacement parameters of calcium and copper is observed. Temperature dependent modelling of the structure, using bond valence concepts, suggests that the calcium atoms become underbonded below approximately 260 K, which provides a rationale for the unusually high Ca displacement parameters at low temperature.