We show that the ground state of Ti 3+ in CsAl alum is a quasi-r 3 state with a very small trigonal splitting. A spin Hamiltonian for this quasi-r 8 state is derived and used to describe the experimental EPR anisotropy. The near cancelation of the trigonal splitting is due to the presence of a dynamic Jahn-Teller effect.The crystal structure of CsAl alum [CsAl(H 2 0) 6 -(S0 4 ) 2 *H 2 0] is cubic with space group Pa3 and four formula units per unit cell. 1 The four [A1(H 2 0)J 3+ octahedra are slightly flattened with trigonal symmetry 5. Recent work on Ti 3+ substituting for Al 3+ in CH 3 NH 3 A1 alum 2 * 3 indicates that the r 5g ground state of Ti 3+ in CsAl alum will show a strong Jahn-Teller coupling to the r 3g vibrational mode. This Letter reports an unusual EPR spectrum and anisotropy for Ti 3+ as a substitutional impurity for Al in CsAl alum which are interpreted below in terms of a quasi-T 8 quartet with a very small trigonal splitting. The trigonal crystal field in CsAl alum is substantial, 1 and the almost complete elimination of the effect of this field is shown to be a direct consequence of the Jahn-Teller coupling of the T 5g electronic state to the r 3g vibrational mode. It arises because the trigonal splitting to first order, which is reduced by the vibronic reduction factor, 4 is comparable with and opposite in sign to the second-order contribution, which involves the excited T 3 g state and is not reduced by any vibronic factor. This Letter also reports the first EPR spectra of and corresponding spin Hamiltonian for a quasi-T 8 quartet with trigonal symmetry.The EPR measurements were performed at
Thin films of Bi 2 Te 3 and PbTe were produced by sputtering using targets of stoichiometric compounds. The compositions of these sputtered thin films were analyzed by the electron microprobe; the Bi2 Te 3 film showed nonstoichiometric compositions of Bi = 44.5 at. %, Te = 55.5 at. %, whereas the compositions ofPbTe films were stoichiometric. The morphology of these sputtered films was established to be polycrystalline by x-ray diffraction (XRD). XRD peaks of Biz Te 3 films revealed the existence of nonstoichiometric crystalline phases; PbTe films have a single cubic phase with (200) preferred orientation. X-ray photoelectron spectroscopy chemical state analysis on both Bi 2 Te 3 and PbTe films showed that Bi, Pb, and Te have one chemical state consistent with the valence state in the compounds. Room temperature carrier concentration and Hall mobility ofBiTe 1 film were measured to be 7.2 X 10 20 em --3 and 15 cm2/V-s respectively; the corresponding values of PbTe films are 5.6X 10 19 cm-3 and 38 cm 2 /V-s, respectively. Doping experiments on Bi2 Te 3 and PbTe films using a single target sputtering system are reported. Sputtered PbTe films doped with Sn have shown promising thermoelectric properties.
Experimental data on the phase relations in the Cu, In, Se system are presented and the growth of single crystals of CuInSe2 from the melt is described. Hall measurements on both n- and p-type crystals reveal that impurity conduction dominates the low-temperature transport properties. Type conversion by annealing of initially n-type crystals in excess selenium vapor leads to a substantial increase in the compensation level.
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