title: Cationic clathrate I Si(46-x)P(x)Te(y) (6.6(1) < or = y < or = 7.5(1), x < or = 2y): crystal structure, homogeneity range, and physical properties.
abstract: A new cationic clathrate I Si(46-x)P(x)Te(y) (6.6(1) < or = y < or = 7.5(1), x < or = 2y at 1375 K) was synthesized from the elements and characterized by X-ray powder diffraction, thermal analysis, scanning electron microscopy, wavelength dispersive X-ray spectroscopy (WDXS), neutron powder diffraction, and (31)P NMR spectroscopy. The thermal behaviors of the magnetic susceptibility and resistivity were investigated as well. Si(46-x)P(x)Te(y) reveals a wide homogeneity range due to the presence of vacancies in the tellurium guest positions inside the smaller cage of the clathrate I structure. The vacancy ordering in the structure of Si(46-x)P(x)Te(y) causes the change of space group from Pm3n (ideal clathrate I) to Pm3 accompanied by the redistribution of P and Si atoms over different framework positions. Neutron powder diffraction confirmed that P atoms preferably form a cage around the vacancy-containing tellurium guest position. Additionally, (31)P NMR spin-spin relaxation experiments revealed the presence of sites with different coordination of phosphorus atoms. Precise determination of the composition of Si(46-x)P(x)Te(y) by WDXS showed slight but noticeable deviation (x < or = 2y) of phosphorus content from the Zintl counting scheme (x = 2y). The compound is diamagnetic while resistivity measurements show activated behavior or that of heavily doped semiconductors. Thermal analysis revealed high stability of the investigated clathrate: Si(46-x)P(x)Te(y) melts incongruently at approximately 1460 K in vacuum and is stable in air against oxidation up to 1295 K.
authors.affiliation: Chemistry Department, Lomonosov Moscow State University, 119991 Moscow, Russia.
authors.forename: J V
authors.initials: JV
authors.lastname: Zaikina
authors.forename: K A
authors.initials: KA
authors.lastname: Kovnir
authors.forename: U
authors.initials: U
authors.lastname: Burkhardt
authors.forename: W
authors.initials: W
authors.lastname: Schnelle
authors.forename: F
authors.initials: F
authors.lastname: Haarmann
authors.forename: U
authors.initials: U
authors.lastname: Schwarz
authors.forename: Yu
authors.initials: Y
authors.lastname: Grin
authors.forename: A V
authors.initials: AV
authors.lastname: Shevelkov