Two-Component Rare-Earth Fluoride Materials with Negative Thermal Expansion Based on a Phase Transition-Type Mechanism in 50 F-'F ( = La-Lu) Systems.

The formation of materials with () based on a () in 50 (temperature-composition) F-'F ( = La-Lu) systems out of 105 possible is predicted. The components of these systems are "" F compounds ( = Pm, Sm, Eu, and Gd) with (), which occur during heating between the main structural types of F: -(β-YF) → -( LaF). The PolTr is characterized by a : the (V) of the low-temperature modification (V) is higher than that of the high-temperature modification (V) by a value (up to 4.7%). In F-F systems, isomorphic substitutions F by forming F () based on both modifications. A ( + ) is a NTE-II material with parameters. The prospects of using the material are estimated using the parameter of the (ΔV/V). The V at a fixed gross composition of a system is determined by the and decay (synthesis) curves and the temperature . The regulation of ΔV/V is achieved by changing within a " Δ". The available Δ values are determined using phase diagrams. A () translates the search for NTE-II materials from 15 F into an array of 105 F-'F systems. Phase diagrams are divided into 10 (s), in four of which NTE-II materials are formed. The tables of the systems that comprise these TypeSs are presented. The position of of the PolTr on the scale for a short () "from PmF to TbF" determines the interval of the Δ offset achievable in the F-F systems: from -148 to 1186 ± 10 °C. NTE-II fluoride materials exceed known NTE-II materials by almost three times in this parameter. Equilibrium in F-F systems is established quickly. The number of qualitatively different two-component fluoride materials with the NTE-II can be increased by more than ten times compared to F with NTE-II.