Full quasi-system “from LaF3 to LuF3” as a combination of 14 binary systems of lanthanide trifluorides with maximal chemical proximity

Abstract

The combination of 15 RF3 (R – rare earth elements – REEs without ScF3 and YF3) into one system “from LaF3 to LuF3” we call a full quasi-system (QS). It consists of 14 serially linked particular systems (PartSs): LaF3–CeF3; CeF3-PrF3; PrF3-NdF3; NdF3-PmF3; PmF3-SmF3; SmF3-EuF3; EuF3-GdF3; GdF3-TbF3; TbF3-DyF3; DyF3-HoF3; HoF3-ErF3; ErF3–TmF3; TmF3-YbF3; YbF3-LuF3. The atomic numbers (Z) of cations from 57 (La) to 71 (Lu) and the temperature (T) are axies of QS. The conditions of including RF3 in PartSs is the neighborhood of R (Ln - lanthanides) positions in Periodic Table of Chemical Elements and |ΔZ| ​= ​1. This securities of maximum chemical proximity (СhProx) of RF3's components. The QS obeys the phase rule, principles of continuity and conformity. Full QS contains all signs of chemical RF3's interactions identified in 34 studied LnF3-Ln’F3 systems. These signs are dependent of ΔZ: perfect and limited isomorphism and two varieties (peritectic and eutectic) of structural true morphotropic transformations (MTs) of phases. Modifications of LnF3 forms the solid solutions (ss) Ln1-xLn'xF3 with average Zav=(1-x)NLn ​+ ​x(N+1)Ln’ (N from 57 to 71). These ss reveal the lanthanide contraction (LC) in the regions |ΔZav|<1. Full QS is an individual sub-level of chemical classification of LnF3-Ln’F3 systems. It is a tool for studies the chemical interactions LnF3, analyzing fine consequences of LC, creating a special system of Ln3+ ionic radii for LnF3, studies of density anomalies (negative thermal expansion), prediction of phase diagrams unexplored systems RF3-R’F3 and other problems of rare earth trifluorides chemical family.