In:
Journal of Materials Chemistry C, Royal Society of Chemistry (RSC), Vol. 9, No. 32 ( 2021), p. 10232-10242
Abstract:
The presence of strongly competing electronic instabilities in a crystalline material can produce fascinating structural phenomena. For example, the A-site-ordered quadruple perovskite BiMn 7 O 12 hosts both active polar instabilities of the Bi 3+ lone pair electrons and Jahn–Teller instabilities of Mn 3+ cations that drive the following sequence of phase transformations on cooling, Im -3 〉 I 2/ m 〉 Im 〉 P 1, corresponding to orbital ordering and polar distortions. Carrier doping by Cu 2+ tunes the two instabilities in BiCu x Mn 7− x O 12 solid solutions and significantly complicates the system behavior. The x = 0.05 and 0.1 members show the following sequence of phase transformations on cooling, Im -3 〉 I 2/ m 〉 R -1(αβγ)0 〉 R 3(00γ) t , and are examples of materials with the electric dipole helicoidal texture in the ground state and a dipole density wave structure in the intermediate R -1(αβγ)0 phase ( Science 2020, 369, 680–684). Here, the detailed behavior of the BiCu x Mn 7− x O 12 solid solutions with x = 0.2–0.8 was investigated by laboratory X-ray, synchrotron X-ray, and neutron powder diffraction between 5 K and 620 K, and differential scanning calorimetry measurements. Nearly every composition (with a step Δ x = 0.1) has a unique behavior when considering both the sequence of phase transitions and the presence of incommensurate superstructure reflections. The sequence Im -3 〉 HT- Immm ( t )* 〉 Immm * 〉 LT- Immm ( t )* is realized for x = 0.2 and 0.3 (where t denotes pseudo-tetragonal), Im -3 〉 I 2/ m * 〉 Immm ( t )* – for x = 0.4, Im -3 〉 I 2/ m * 〉 I 2/ m * – for x = 0.5, Im -3 〉 I 2/ m * 〉 Im -3 – for x = 0.6 and 0.7, and Im -3 〉 R -3 〉 I 2/ m 〉 Im -3 – for x = 0.8, where asterisks denote the presence of additional incommensurate reflections. Re-entrance of the high-temperature cubic phase was observed at low temperatures for x = 0.6–0.8 suggesting strong competition between the different electronic instabilities. The re-entrant cubic phases have nearly zero thermal expansion.
Type of Medium:
Online Resource
ISSN:
2050-7526
,
2050-7534
Language:
English
Publisher:
Royal Society of Chemistry (RSC)
Publication Date:
2021
detail.hit.zdb_id:
2702245-6
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