Indirect nuclear exchange coupling and electronic structure of the layered semiconductor TlS: NMR study and band structure calculation

Abstract

We have studied the electronic structure of the layered semiconductor TlS by means of 203 Tl and 205 Tl NMR and band structure calculation. The crystal structure of this compound is built from the metal-chalcogen layers formed of linked Tl 3+ S 2− 4 tetrahedra and Tl + ions located between the layers. Our experiments show significant interlayer indirect exchange coupling of thallium nuclei. Since the distances between thallium ions essentially exceed the sum of their ionic radii, it is concluded that such coupling is realized due to the overlap of the Tl electron wavefunctions across the intervening S atom. The exchange interaction has been evaluated by means of the quantitative spectral analysis. The band structure calculation shows that the top of the valence band is composed of mixed Tl + 6s6p z -S 3s3p z -Tl 3+ 6s6p z states, yielding overlap of the Tl + -S-Tl 3+ type. Such electronic structure gives rise to the effective interlayer coupling of Tl nuclear spins observed in the experiment. This effect is discussed along with the recently obtained NMR results in the chain thallium sulfide and selenide.

Electrical switching studies on Ge–Te–Tl chalcogenide glasses: Effect of thallium on the composition dependence of switching voltages

“…However NMR studies on similar samples of Tl-As-Se [20] have indicated the possibility that thallium can enter the network with either a valency of one or three. NMR on the crystalline chalcogenides containing thallium [21,22] also indicates two valencies for the thallium. The chemical shift values tend to indicate that the valency of one leads to a bonding similar to that in thallous chloride which is ionic in nature.…”

Thermal diffusivity measurements on ternary Ge–Te–Tl glasses using Photo-thermal Deflection method: Effect of thallium addition

“…This idea of two valencies for thallium is suggested on the basis of 205 Tl NMR studies on amorphous As-Se-Tl samples [24]. Thallium NMR of crystalline ternary chalcogenides containing thallium also indicate the presence of these two types of valencies for thallium [25,26].…”

Size-dependent properties ofTl2Sestudied by NMR spectroscopy

“…We measured NMR spectra and spin-lattice relaxation rates of 203 Tl and 205 Tl isotopes, that have spin I =1/2 and are excellent probes in studying the electronic structure of compounds. [1][2][3][4][5][6][7][8][9][10][11][12][13] Our measurements show clear distinction in the indirect nuclear exchange coupling and Knight shift in the bulk and nanorod Tl 2 Se samples, reflecting noticeable difference in their electronic structure. Though Mooser and Pearson 14 mentioned that bulk Tl 2 Se behaves as a metal, we observed that it exhibits Korringa-like spin-lattice relaxation behavior only at low temperatures.…”

“…6 MHz, corresponding to the Larmor frequency of 205 Tl isotope in the magnetic field B 0 = 1.17 T. The large S 2 values observed imply that the line shape is related to essential indirect nuclear exchange interactions among the Tl nuclei that are characteristic for most of Tlcontaining compounds. [1][2][3][4][5][6][7][8][9][10][11][12][13] Van Vleck has shown 19 that in the exchange-coupled nuclear systems, described by the Hamiltonian Ĥ = J jk I j I k , only exchange interaction between unlike spins contributes to the second moment of the NMR spectrum. Therefore in a crystal that contains two different isotopes, the ratio of their second moments is inversely proportional to the ratio of the isotope contents.…”

“…Taking into account that each Tl atom has 12 nearest Tl neighbors, we found J Tl-Tl = 21 kHz that is characteristic of thallium compounds. [1][2][3][4][5][6][7][8][9][10][11][12][13] In bulk Tl 2 Se, the signals of two isotopes overlap due to the large line widths, and their second moments are hardly determined. The larger line width in bulk Tl 2 Se indicates larger exchange interaction in comparison with that in nanorods.…”