The role of lattice distortions in determining the thermal properties of electron doped CaMnO(3).

ABSTRACT

We have investigated the thermal properties of electron doped perovskite manganite CaMnO(3), the end member ([Formula see text]) of the Ruddlesden-Popper (RP) calcium manganates series with cation doping at the A-site. In this paper the functional relation between the lattice distortions and the thermal properties is determined and compared to available reports. The temperature dependence of the lattice specific heat (C(v(lattice))) of Ca(1-x)Ln(x)MnO(3) (x = 0.05, 0.10, 0.15, 0.20) with Ln(= La, Ce, Pr, Nd, Th, Bi) doping at the A-site has been studied as a function of temperature (10 K≤T≤500 K) by means of a rigid ion model (RIM) after modifying its framework to incorporate the van der Waals interactions. Strong electron-phonon interactions are present in these compounds, which are responsible for the variation of the lattice specific heat with cation doping of varying size and valency. We have found that the calculated thermal properties reproduce well the corresponding experimental data, implying that modified RIM represents properly the nature of these perovskite manganite systems. We demonstrate that the electron concentration, size mismatch and Jahn-Teller (JT) effects are the dominant factors, whereas charge mismatch and buckling of Mn-O-Mn angle influence the thermal properties to a lesser degree in the ferromagnetic state. In the insulating paramagnetic state, JT distortions vary linearly and influence the thermal properties. These specific heat results can be further improved by including the ferromagnetic spin wave and charge order contributions to the specific heat.