Gd₄Ge_3–<i>x</i><i>Pn</i>_<i>x</i> (<i>Pn</i> = P, Sb, Bi, <i>x</i> = 0.5–3): Stabilizing the Nonexisting Gd₄Ge₃ Binary through Valence Electron Concentration. Electronic and Magnetic Properties of Gd₄Ge_3–<i>x</i><i>Pn</i>_<i>x</i>

Abstract

Gd₄Ge_3–<i>x</i><i>Pn</i>_<i>x</i> (<i>Pn</i> = P, Sb, Bi; <i>x</i> = 0.5–3) phases have been prepared and characterized using X-ray diffraction, wavelength-dispersive spectroscopy, and magnetization measurements. All Gd₄Ge_3–<i>x</i><i>Pn</i>_<i>x</i> phases adopt a cubic anti-Th₃P₄ structure, and no deficiency on the Gd or <i>p</i>-element site could be detected. Only one P-containing phase with the Gd₄Ge_2.51(5)P_0.49(5) composition could be obtained, as larger substitution levels did not yield the phase. Existence of Gd₄Ge_2.51(5)P_0.49(5) and Gd₄Ge_2.49(3)Bi_0.51(3) suggests that the hypothetical Gd₄Ge₃ binary can be easily stabilized by a small increase in the valence electron count and that the size of the <i>p</i> element is not a key factor. Electronic structure calculations reveal that large substitution levels with more electron-rich Sb and Bi are possible for charge-balanced (Gd³⁺)₄(Ge^4–)₃ as extra electrons occupy the bonding Gd–Gd and Gd–Ge states. This analysis also supports the stability of Gd₄Sb₃ and Gd₄Bi₃. All Gd₄Ge_3–<i>x</i><i>Pn</i>_<i>x</i> phases order ferromagnetically with relatively high Curie temperatures of 234–356 K. The variation in the Curie temperatures of the Gd₄Ge_3–<i>x</i>Sb_<i>x</i> and Gd₄Ge_3–<i>x</i>Bi_<i>x</i> series can be explained through the changes in the numbers of conduction electrons associated with Ge/Sb­(Bi) substitution