Phase Equilibrium in the System Ln-Mn-O at 1100℃ : IX. Ln=Er and Tm

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Phase equilibrium was established in a Ln-Mn-O (Ln=Er and Tm) system at 1100℃ with the oxygen partial pressure ranging from -log (Po_2/atm)=0 to 12.00, and phase diagrams for the corresponding Ln_2O_3-MnO-MnO_2 system at 1100℃ were constructed. Stable Er_2O_3, MnO, Mn_3O_4, and ErMnO_3 phases were found in the Er-Mn-O system, and stable Tm_2O_3, MnO, Mn_3O_4, and TmMnO_3 phases were found in the Tm-Mn-O system. LnMn_2O_5, Ln_2Mn_2O_7, Ln_2MnO_4, Mn_2O_3, and MnO_2 were not found in either system. Nonstoichiometric ranges were found in both LnMnO_3 phases, with the composition of LnMnO_3 represented as functions of log (Po_2/atm), No/N_<ErMnO_3>=2.68×10^<-3> (log Po_2)-0.008 and No/N_<TmMnO_3>=2.53×10^<-3>log (Po_2)-0.005 The activities of the components in a solid solution were calculated from the both equations. The lattice constants of ErMnO_3 and TmMnO_3 quenched in air were determined. The standard Gibbs energy changes of the reaction, 1/2 Ln_2O_3+MnO+1/4 O_2=LnMnO_3, appearing in the phase diagrams were also calculated. The relationship between the tolerance factors (t) of ErMnO_3, TmMnO_3 and ΔG^0 values of the reaction, 1/2 Ln_2O_3+MnO+1/4 O_2=LnMnO_3, was shown graphically, together with other previous LnMnO_3 values. The two present ΔG^0 values were well-fitted to the general equation for hexagonal LnMnO_3, ΔG^0 (hexa)=-6.426×10^2t+5.406×10^2, which was previously obtained.
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