The system thorium-palladium-boron: A DFT study on the stability and properties of Th2Pd15B5

Electronic and Structural Properties of MPtxB6–2x (M = Y, Yb): Structural Disorder in an Octahedral Boron Framework

“…The composition of the new phase YPt x B 6–2 x , as refined from single-crystal XRD data, is close to the composition of the so-called “21 K superconducting phase” Th 1– y Pd x B 6–2 x ( x = 0.65, 0 ≤ y ≤ 0.22), which was described by Zandbergen et al in 1995 from high-resolution electron microscopy and which was recently reported to be the end point of the Th­(B,Pd) 6 solid solution, terminating at 9 at. % Pd at 950 °C . In contrast to thorium palladium boride, YPt x B 6–2 x at 780 °C is a free-standing ternary compound according to EPMA and powder XRD (Figures , S15–S17, Table S2).…”

“…% Pd at 950 °C. 52 In contrast to thorium palladium boride, YPt x B 6−2x at 780 °C is a free-standing ternary compound according to EPMA and powder XRD (Figures 9, S15−S17, Table S2). This compound forms two phase equilibria with three ternary phases YPt 27,28,34 further studies on the boron-rich part of the Y−Pt−B phase diagram, with emphasis on crystal structure and properties of ternary higher borides are in progress.…”

“…Hexaborides readily form solid solutions with one another; moreover, the distribution of metal atoms throughout the boron sublattice have been proposed for certain systems, i.e., for 21 K superconductor ThPd x B 6–2 x (space group Pm 3̅ m , a = 4.2 Å, x = 0.65) − and nonsuperconducting YPd 1.2 B 3.3 [cubic, a = 4.2 Å, with an incommensurate modulation vector q = 0.285 ( a * + b * + c *)] . Lately, the solubility of Pd in ThB 6 has been explored employing the WDX-EPMA and X-ray powder diffraction data of alloys annealed at 950 °C; a continuous solid solution Th 1– y Pd x B 6–2 x terminating at composition Th 17.2 Pd 9.0 B 73.8 (in at. %) was found to form which approximately corresponds to that reported for the 21 K superconductor ThPd x B 6–2 x . − Actually, no significant alterations of lattice parameters at about 10 at.…”

“…%) was found to form which approximately corresponds to that reported for the 21 K superconductor ThPd x B 6–2 x . − Actually, no significant alterations of lattice parameters at about 10 at. % Pd solubility for the solid solution Th 1– y B 6 (0 ≤ y ≤ 0.22)–Th 1– y Pd x B 6–2 x ( x ≤ 0.65; 0 ≤ y ≤ 0.22 for x = 0) ( a = 4.110–4.115 Å) in comparison with Th 1– y B 6 ( a = 4.112 Å) were observed from Rietveld refinement of powder X-ray diffraction data of three phase alloys . Since the accurate boron content and boron atom positions are difficult to be refined unambiguously from high-resolution electron microscopy, electron diffraction, (WDX-) EPMA, and X-ray powder diffraction data in boride structures that consist of heavy metal atoms next to light boron atoms, further precise studies of MPd x B 6–2 x or related systems employing single-crystal X-ray diffraction were extremely desired.…”

“…% Pd solubility for the solid solution Th 1– y B 6 (0 ≤ y ≤ 0.22)–Th 1– y Pd x B 6–2 x ( x ≤ 0.65; 0 ≤ y ≤ 0.22 for x = 0) ( a = 4.110–4.115 Å) in comparison with Th 1– y B 6 ( a = 4.112 Å) were observed from Rietveld refinement of powder X-ray diffraction data of three phase alloys. 52 Since the accurate boron content and boron atom positions are difficult to be refined unambiguously from high-resolution electron microscopy, electron diffraction, (WDX-) EPMA, and X-ray powder diffraction data in boride structures that consist of heavy metal atoms next to light boron atoms, further precise studies of MPd x B 6–2 x or related systems employing single-crystal X-ray diffraction were extremely desired. Furthermore, electronic properties of hexaborides originate from the crystal structure, in which the covalently bonded boron atoms surround the metal atom, which donate electrons to the charge-deficient boron framework; it has been shown by band gap calculations that very low levels of doping cause the changes in B–B intra- and interoctahedra distances and affect the electronic properties.…”