Bismuth- and Iron-Substituted Lanthanum Manganite: Synthesis and Structure

Abstract

The detailed study of the solid solutions with the general composition La_{1 − x}Bi_xMn_{1 − y}Fe_yO_{3 + δ} (x = 0.1–0.3, y = 0.1–0.3) prepared by means of solid-phase synthesis has been performed for the first time. The synthesized samples crystallize in an R-centered trigonal unit cell at room temperature and have the oxygen nonstoichiometry index δ = 0.15. The existence of two types of crystallites with related but yet different space groups has been established for La_0.7Bi_0.3Mn_0.9Fe_0.1O_{3 + δ} by high-resolution transmission electron microscopy. All the samples experience chemical expansion at temperatures above 650°C. The thermal expansion coefficient is 11.6 × 10⁻⁶°C⁻¹ in the low-temperature region (25–650°C) and 12.3 × 10⁻⁶°C⁻¹ in the high-temperature region (650–1000°C). The electroconductivity of all the studied solid solutions in the temperature range 800–200°C is slightly lower than for undoped lanthanum manganite.