Phase coexistence in Bi1−x Pr x FeO3 ceramics

Abstract

Bi 1-x Pr x FeO 3 ceramics across the rhombohedral-orthorhombic phase boundary have been studied by X-ray diffraction, transmission electron microscopy and differential scanning calorimetry. The structural phase transitions in Bi 1-x Pr x FeO 3 driven by doping concentration and temperature are significantly different from those in BiFeO 3 compounds doped with other rareearth elements. The features of the structural transformations have been discussed based on the specific character of the chemical bonds associated with praseodymium ions. The detailed study of the crystal structure evolution clarified the ranges of both single phase and phase coexistence regions at different temperatures and dopant concentrations. For x=0.125 compound the threephase coexistence region has been observed in the narrow temperatures range about 400 o C. The results explicate driving forces of the structural transitions and elucidate the origin of the remarkable physical properties of BiFeO 3 -based compounds near the morphotropic phase boundary.

First-principles study of structural, electronic, and ferroelectric properties of rare-earth-doped BiFeO3

“…-1 as listed in Table 2) for Bi 0.875-Pr 0.125 FeO 3 . According to Karpinsky et al [55,56], the R3c and Pnam phases in Bi 1-x Pr x FeO 3 samples coexist in the concentration region 0.12 \ x\0.15. The energy differences between R3c and Pnma, R3c and Pn2 1 a phases for BiFeO 3 systems with La-, Ce, and Nd-substitution of Bi are above 20 eV f.u.…”

Теплоемкость мультиферроиков Bi-=SUB=-1-x-=/SUB=-Pr-=SUB=-x-=/SUB=-FeO-=SUB=-3-=/SUB=-

“…В ин-тервале 0.20 < x ≤ 0.30 фаза R3c исчезает и сосуще-ствуют две фазы: P 1 и P 2 . Подобное наблюдалось при исследованиях твердых растворов Bi 1−x La x FeO 3 [4] и Bi 1−x Pr x FeO 3 [5][6][7]. При анализе экспериментальных данных по тепло-емкости в широком интервале температур необходимо учитывать ангармонический вклад в фононную теп-лоемкость.…”

“…В работах [5,6] показано, что при повышении температуры в составах Bi 1−x Pr x FeO 3 может формироваться двух-и трехфазное структурное состоя-ние (стабильное в определенном интервале температур), при котором сосуществуют ромбоэдрическая и орто-ромбические фазы. Все это стимулирует дальнейшие подробные исследования мультиферроиков на основе феррита висмута, легированного редкоземельными эле-ментами.…”

Intermediate structural state in Bi1−x Pr x FeO3 ceramics at the rhombohedral–orthorhombic phase boundary

“…Among the BiFeO3-based materials doped with rare-earth elements, solid solutions with praseodymium ions show the most intriguing evolution of the crystal structure as a function of temperature. For instance, the existence of the three-phase region has been declared for the Prdoped compounds at temperatures about 380 °C Ref [10], and the authors have justified it in terms of thermodynamically non-equilibrium state. The obtained structural data specify a number of structural transitions occurred in a narrow temperature range as well as the phase coexistence regions.…”

“…In BiFeO3, chemical replacement of Bi 3+ with the rare-earth elements possessing comparable ionic radius (La 3+ -Eu 3+ ) causes the concentration-driven structural transition from the polar rhombohedral to the nonpolar orthorhombic phase that occurs via the formation of the antipolar orthorhombic structure [4,[6][7][8][9][10][11]. Most promising physical parameters were obtained for the lanthanum and praseodymium-doped compounds within the morphotropic phase boundary region [3,8,12], the phase coexistence range estimated for these compounds is stable over a very broad compositional range (Δx~5%) far exceeding those attributed to the compounds doped with other rare-earth elements [4,7].…”