Solid-state tellurium-125 nuclear magnetic resonance studies of transition-metal ditellurides †

125Te NMR chemical shifts and tellurium coordination environments in crystals and glasses in the Ge–As–Sb–Te system

“…Hence, the assignment of the 125 Te NMR chemical shift range of 650 to 1050 ppm to two-coordinated Te atoms in these binary Ge-Te and As-Te glasses is consistent with the abovementioned trend of increasing chemical shift for 125 Te with decreasing Te coordination number. It is also consistent with the 125 Te NMR isotropic chemical shift of 1005 ppm for the 2-coordinated TeTe-Te sites in pure crystalline Te, as reported by Orion et al [4,26].…”

“…2 and 4) that the line broadening in the 125 Te wideline NMR spectrum of this material arises primarily from large shielding anisotropies. As shown in a previous 125 Te NMR spectroscopic study of transition metal tellurides [4], such shielding anisotropies may have contributions from both shielding interaction of bonding electrons around the Te atom as well as from hyperfine interaction between delocalized electrons and the Te nuclide in conducting samples. A secondary line broadening mechanism may be dipolar in origin in this system.…”

“…This effect of increasing coordination on NMR chemical shift is typical of a number of nuclides including 29 Si, 27 Al and 11 B [1,2]. Moreover, the 125 Te NMR chemical shifts of 6-coordinated Te atoms in MTe semiconductors (M = Hg, Zn, Cd, Pb and Sn) are also located several thousand ppm on the high field side compared to 3-coordinated Te atoms in transition metal ditellurides [4].…”

“…The increment of the spectrometer frequency was chosen on the basis of the π/2 pulse length and probe characteristics such as the quality factor of the rf coil in order to ensure a uniform rf excitation profile over the entire sweep width of 1 MHz. The conducting crystalline samples were mixed with insulating SiO 2 powder in order to enhance penetration of the radio frequency fields and improve the probe tuning [4]. 125 Te MAS NMR spectra were collected at multiple spinning speeds ranging between 10 and 30 kHz for the As 2 Te 3 crystal sample using a ZrO 2 rotor and a Bruker 2.5 mm CPMAS probe.…”

“…However, it is also characterized by a long spin-lattice relaxation time T 1 and displays a large chemical shift range of several thousands of ppm that can make high-resolution 125 Te NMR spectroscopy in the solid state experimentally challenging [4]. Nevertheless, 125 Te solid state NMR spectroscopy has been used extensively for establishment of its chemical shift scale and structural characterization of Te coordination environments in inorganic tellurium salts, MTe (M = Pb, Zn) semiconductors, tellurium oxide based (tellurite) crystals and glasses, transition metal tellurides and organo-metallic compounds [4][5][6][7][8]. However, the chemical shift systematics of 125 Te remain practically unexplored in crystalline and amorphous chalcogenide materials in the Ge-Sb-As-Te system.…”