Formation enthalpies of LaLn׳O3 (Ln׳=Ho, Er, Tm and Yb) interlanthanide perovskites

Abstract

High-temperature oxide melt solution calorimetry using 3Na 2 O·MoO 3 at 802 °C was performed for interlanthanide perovskites LaLn'O 3 (Ln' = Ho, Er, Tm and Yb) and lanthanide oxides (). The enthalpies of formation of these interlanthanide perovskites from binary lanthanide oxides at room temperature (25 ºC) were determined to be -8.30 ± 3.40 kJ/mol for LaHoO 3 , -9.85 ± 3.04 kJ/mol for LaErO 3 , -10.80 ± 2.71 kJ/mol for LaTmO 3 and -12.33 ± 2.94 kJ/mol for LaYbO 3 . There is a roughly linear relationships between these enthalpy values and the tolerance factor for these and for other LaM 3+ O 3 (M = In, Sc, Ga, Al, Fe and Cr) perovskites, confirming that the distortion of the perovskites as results from ionic radius difference of A-site and B-site cations, is the main factor determining the stability of these compounds.

Thermodynamic Stability of Transition‐Metal‐Substituted LiMn2−xMxO4 (M=Cr, Fe, Co, and Ni) Spinels

“…Substitution of Mn 3+ by an M 3+ with an ionic radius that is closer to that of Mn 4+ , decreases the lattice parameters and may relax and stabilize the spinel structure, resulting in a more exothermic formation enthalpy from oxides. Analogous trends have been reported in garnet and perovskite systems. The substitution of Ni 2+ ions (0.69 Å), which have the largest ionic radius of the dopants in this study, into LiMn 4+ 1.5 Ni 2+ 0.5 O 4 causes increased thermodynamic stability compared with LiMn 4+ Mn 3+ O 4 , which is opposite to the trend observed in Co‐substituted and Cr‐substituted systems.…”

Thermodynamics of solid phases containing rare earth oxides

“…They have been investigated intensively because of their useful electrical and magnetic properties [8; 9]. Double rare earth perovskites, with a larger RE on the A-site and a smaller one on the B-site are of marginal thermodynamic stability but their energetics fit the trend of enthalpy vs. tolerance factor defined by more stable perovskites [10].…”

Thermal Analysis of High Entropy Rare Earth Oxides

“…All the studied systems of trivalent rare earth oxides are characterized by wide ranges of solid solutions in the structures identified in pure oxides. Eleven interlanthanide perovskites are known to form in several systems combining large and small rare earths: LaRO 3 (R = Y, Ho-Lu), CeRO 3 (R = Tm-Lu), and PrRO 3 (R = Yb-Lu) [ 37 , 38 , 39 ]. They all show an orthorhombic ( Pnma ) distortion and do not melt congruently, but decompose at 800–2000 °C into solid solutions of one of rear earth oxide structure types [ 39 ].…”