Dysprosium doping of Ca2MnO4: Effect on crystal structure at room temperature and thermal behavior

Dysprosium-doped Ruddlesden-Popper calcium manganates with compositions of Ca2-xDyxMnO4 are potential candidates for high temperature thermoelectric applications. The effect of dysprosium doping on the crystal structure of Ca2-xDyxMnO4 at room temperature and its thermal behavior between RT and 800 degrees C were investigated in the range 0 < x < 0.2 by Rietveld analysis of RT- and HT- X-ray powder diffraction data. The Rietveld analysis confirmed the compatibility of all the analyzed compounds with the I41/acd space group. Ca2+ substitution by Dy3+, electrically balanced by the reduction of an equivalent amount of Mn4+ to Mn3+, leads to an increase of the a parameter and a decrease of the c parameter. No phase transition was observed from RT to 800 degrees C but we show that several complex structural mechanisms lead to a strong anisotropic thermal expansion.