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The High‐Pressure Oxide Tb 3 O 5 and its Non‐Centrosymmetric Low‐Temperature Polymorph–A Comprehensive Study
Author(s) -
Glätzle Matthias,
Janka Oliver,
Svitlyk Volodymyr,
Chernyshov Dmitry,
Bartsch Manfred,
Zacharias Helmut,
Pöttgen Rainer,
Huppertz Hubert
Publication year - 2018
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201804006
Subject(s) - orthorhombic crystal system , antiferromagnetism , crystallography , metastability , crystal structure , paramagnetism , oxide , chemistry , powder diffraction , curie temperature , magnetic moment , space group , materials science , diffraction , x ray crystallography , condensed matter physics , ferromagnetism , metallurgy , physics , organic chemistry , optics
In this article, the first thoroughly characterized mixed‐valent binary rare earth oxide synthesized under high‐pressure/high‐temperature conditions, and its low‐temperature polymorph are reported. Crystalline HT‐HP‐Tb 3 O 5 has been prepared from an equimolar mixture of Tb 4 O 7 and Tb 2 O 3 under reaction conditions of 8 GPa and 1323 K. Single‐crystal X‐ray structure determination showed that HT‐HP‐Tb 3 O 5 crystallizes in the orthorhombic space group Pnma , isopointal to the β‐Yb 5 Sb 3 ‐type structure. Temperature‐dependent measurements of the magnetic susceptibility showed that HT‐HP‐Tb 3 O 5 is a Curie–Weiss paramagnet. The observed effective magnetic moment of μ eff =9.21(2) μ B per formula unit fits well to the calculated moment of μ calc =9.17 μ B . Low‐field measurements revealed antiferromagnetic ordering at T N =3.6(1) K. Heat capacity measurements indicated an intrinsic structural phase transition of HT‐HP‐Tb 3 O 5 at low temperature, which was confirmed by synchrotron X‐ray powder diffraction data recorded at 2 K. The metastable high‐pressure modification HT‐HP‐Tb 3 O 5 undergoes a translationengleiche transition from space group Pnma to Pn 2 1 a (non‐standard setting of Pna 2 1 ), leading to the low‐temperature polymorph LT‐HP‐Tb 3 O 5 by loss of a mirror plane (displacive phase transition).