R5Pn3-type Phases of the Heavier Trivalent Rare-Earth-Metal Pnictides (Pn=Sb, Bi): New Phase Transitions for Er5Sb3 and Tm5Sb3
The syntheses and distributions of binary R{sub 5}Pn{sub 3} phases among the hexagonal Mn{sub 5}Si{sub 3} (M), and the very similar orthorhombic {beta}-Yb{sub 5}Sb{sub 3} (Y) and Y{sub 5}Bi{sub 3} (YB) structure types have been studied for R = Y, Gd-Lu and Pn = Sb, Bi. Literature reports of M and YB-type structure distributions among R{sub 5}Pn{sub 3} phases, R = Y, Gd-Ho, are generally confirmed. The reported M-type Er{sub 5}Sb{sub 3} could not be reproduced. Alternate stabilization of Y-type structures by interstitials H or F has been disproved for these nominally trivalent metal pnictides. Single crystal structures are reported for (a) the low temperature YB form of Er{sub 5}Sb{sub 3} (Pnma, a = 7.9646(9) {angstrom}, b = 9.176(1) {angstrom}, c = 11.662(1) {angstrom}), (b) the YB- and high temperature Y-types of Tm{sub 5}Sb{sub 3} (both Pnma, a = 7.9262(5), 11.6034(5) {angstrom}, b = 9.1375(6), 9.1077(4) {angstrom}, c = 11.6013(7), 7.9841(4) {angstrom}, respectively), and (c) the YB structure of Lu{sub 5}Sb{sub 3}, a = 7.8847(4) {angstrom}, b = 9.0770(5) {angstrom}, c = 11.5055(6) {angstrom}. Reversible, temperature-driven phase transitions ({beta}-Yb{sub 5}Sb{sub 3} Y{sub 5}Bi{sub 3} types) for the former Er{sub 5}Sb{sub 3} and Tm{sub 5}Sb{sub 3} around 1100 C and the means of quenching the high temperature Y form, have been established. According to their magnetic susceptibilities, YB-types of Er{sub 5}Sb{sub 3} and Tm{sub 5}Sb{sub 3} contain trivalent cations. Tight-binding linear muffin-tin-orbital method within the atomic sphere approximation (TB-LMTO-ASA) calculations for the two structures of Tm{sub 5}Sb{sub 3} reveal generally similar electronic structures but with subtle Tm-Tm differences supporting their relative stabilities. The ambient temperature YB-Tm{sub 5}Sb{sub 3} shows a deep pseudogap at EF, approaching that of a closed shell electronic state. Short R-R bonds (3.25-3.29 {angstrom}) contribute markedly to the structural stabilities of both types. The Y-type structure of Tm{sub 5}Sb{sub 3} shows both close structural parallels to, and bonding contrasts with, the nominally isotypic, stuffed Ca{sub 5}Bi{sub 3}D and its analogues. Some contradictions in the literature are discussed.
- Research Organization:
- Ames Lab., Ames, IA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- DE-AC02-07CH11358
- OSTI ID:
- 977248
- Report Number(s):
- IS-J 7498; TRN: US201013%%450
- Journal Information:
- Inorganic Chemistry, Vol. 48, Issue 10
- Country of Publication:
- United States
- Language:
- English
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