The dependence of polymorphism on the ionic radius of Ln3+ (LnLaEr, Y) in the oxide ion conductors Bi0.775Ln0.225O1.5

Structural and Conductivity Properties of Bi0.775Ln0.225O1.5Oxide Conductors (Ln=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy) with Rhombohedral Bi–Sr–O Type

“…For¸n"Gd, Tb, and Dy, the formation of an fcc phase occurs between 700 and 900°C and is preserved at room temperature when the sample is quenched; this is in a fairly good agreement with the previous thermal investigation of these materials using a Guinier-Lenne`camera (7). In this previous study, the absence of formation with¸n"Pr and Nd and the reversibility of the transformation for¸n "Gd was signaled.…”

“…This suggests that it should be considered as previously done on the basis of the unit cell volume evolution (7), that all these phases exhibit the structural type. The two different observed evolutions could also correspond to a first set of -type samples (¸n"La, Pr, Nd, Sm, Eu) and a second set of type in which the cations of the mixed layer are disordered; this would be in agreement with the absence of P transition, particularly for¸n"Tb and Dy (7).…”

“…A systematic investigation of specific compositions Bi ¸n O (¸n"La, Pr, Nd, Sm, Eu, Gd, Tb, Dy) selected as the reference, has been made in order to check the rhombohedral polymorphism (7). Different types of evolutions, depending on the¸n nature, are obtained upon heating of the low temperature form: one leads to the closely related high temperature form for¸n"La-Sm ( #fcc -Bi O -related phase mixture for¸n"Eu, Gd) and further to a fcc -Bi O -related phase for¸n"Sm-Gd; another goes directly to this fcc structural type (¸n" Tb-Er); in this case the P transformation appears irreversible under dynamic cooling conditions (cooling rate 55°C min\).…”

Phase Relations in the System BiO1.5–YbO1.5–CuO

“…No monoclinic phase (7), orthorhombic phase (8), rhombohedral phase (9), or solid solution (10), which were reported in other BiO -RO systems, were found in the present system.…”

Evidence for a New Monoclinic Bi–La Oxide Solid Solution: Identification and Structural Relationship to the Rhombohedral Bi–Sr–O Type

“…A high-temperature form ( ) with an hexagonal closely related structure is generally observed. The P transition, which occurs in all cases with a fast increase of conductivity, is accompanied by a sudden enlargement of the cell parameters (7,8,12,19), which can be attributed to a cationic disordering in the mixed layer and to the migration of the O ions toward the interslab space. When reported, the evolution versus composition of the transition temperature and enthalpy, the isothermal conductivities and activation energies of , and the expansion of c-cell parameter during transition, exhibit either maxima or minima values; for Bi O }MO systems, these extrema have been linked to the existence of one (M"Ca, Ba) or two (M"Sr) kinds of cationic ordering in the mixed sandwiched layers of the form, leading to one or two kinds of superstructure.…”