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Preparation, Crystal Structure, Properties, and Electronic Band Structure of Tltase3 Christoph L Preparation, Crystal Structure, Properties, and Electronic Band Structure of TlTaSe3 Christoph L. Teskea, Wolfgang Benscha, Diana Beneab, Jan Min´arb, Alexander Perlovb, and Hubert Ebertb a Institut f¨ur Anorganische Chemie, Christian-Albrechts-Universit¨at, Otto-Hahn-Platz 6/7, D-24098 Kiel, Germany b M¨unchen, Department Chemie – Physikalische Chemie, Ludwigs-Maximilians-Universit¨at, Butenandtstraße 11, D-81377 M¨unchen Reprint requests to Dr. C. Teske. Fax: +49 431 880 1520. E-mail: [email protected] Z. Naturforsch. 60b, 858 – 866 (2005); received June 10, 2005 TlTaSe3 was prepared from a fused mixture of Tl4Ta2Se11, Ta and Se in the molar ratio 1:2:1. The compound shows dimorphism with H-TlTaSe3, hexagonal, space group P63/mmc, a = 7.2436(6), c = 5.9736(6) A,˚ c/a = 1.213 and O-TlTaSe3, orthorhombic, space group Pnma, a = 9.554(13), b = 3.6244(6), c = 14.7271(17) A.˚ The crystal structure of H-TlTaSe3 is isotypic to BaVSe3 whereas that of O-TlTaSe3 is closely related to the NH4CdCl3-type. Characteristic features of the structures are: 1 2− ∞[TaSe3 ] chains of regular octahedra sharing faces along [001] for the hexagonal form and columns 1 2− of double edge-sharing octahedra ∞[Ta2Se6 ] running along [010] for O-TlTaSe3. The columns are each separated by Tl+ ions with the coordination number CN = 12 and CN = 8 respectively. The structures are compared and discussed in context with other isotypic structures of chalcogenides. The orthorhombic modification O-TlTaSe3 is a semiconductor while H-TlTaSe3 shows conventional metallic behaviour. The electronic structures of both modifications are discussed on the base of band structure calculations performed within the framework of density functional theory. Key words: Thallium Tantalum Selenide, Crystal Structure, Dimorphic, Properties, Electronic Band Structure Introduction electronic band structure, and some physical properties of TlTaSe3. Recently we reported on the preparation, struc- ture and physical properties of TlTaS3 [1]. This com- Experimental Section pound was prepared by reacting mixtures of Ta pow- Preparation der, Tl2S and sulphur in sealed glass tubes in a tem- ◦ ◦ perature range 445 C ≤ T ≤ 495 C. The investiga- The starting materials were Ta powder (99,7% Riedel- tions revealed an orthorhombic structure closely re- De Ha¨en AG), Tl4Ta2Se11 [3] and Se powder (grey, Riedel- lated to the NH4CdCl3-type (Strukturberichte, type De Ha¨en AG). The selenide was prepared from a mixture of E24) having columns of double edge-sharing octahe- appropriate amounts of Ta and Se with Tl4Ta2Se11 [3] (2:1:1) − 1 2 to give the composition TlTaSe3. This mixture was reacted in dra ∞[Ta2Se6 ]. TlTaS3 is a semiconductor with a nar- ≈ . a flame-sealed glass (DURAN R ) ampoule (argon, reduced row optical band gap Eg 0 78 eV. In addition, a Nu- ◦ clear Magnetic Resonance study of 203Tl and 205Tl was pressure) at 480 C. Starting with a black thin liquid melt the sample began to crystallise after a few hours yielding af- carried out [2]. These results show noticeable intra- ter four days an anthracite bulk of microcrystalline TlTaSe . chain (Tl-Tl) and inter-chain (Tl-Ta) indirect nuclear 3 All attempts to prepare single crystals at elevated tempera- spin-spin interactions. These findings lead to the ques- tures suitable for X-ray investigations were not successful. tion whether the homologous selenide can be prepared Rising the temperature above approximately 550 ◦C pro- and whether it shows the same structural and physical motes decomposition as confirmed by X-ray powder diffrac- properties. In the present article, results of pertinent ex- tion and thermal investigations. Finally, single crystals could perimental and theoretical investigations are presented. be grown from a solution in molten TlBr. A mixture of pow- In particular, we report on the preparation, structure, dered TlTaSe3 (prepared as mentioned above) and TlBr (mo- 0932–0776 / 05 / 0800–0858 $ 06.00 c 2005 Verlag der Zeitschrift f¨ur Naturforschung, T¨ubingen · http://znaturforsch.com C. L. Teske et al. · Preparation, Crystal Structure, Properties, and Electronic Band Structure of TlTaSe3 859 No. 2θobs hkl 2θcalc ∆2θ Irel. dobs dcalc Table 1. X-ray powder diffrac- *1 13.94000213.921 0.0189 22.9 6.3477 6.3563 tion pattern for H-TlTaSe3. 2 14.10210014.107 −0.0047 45.8 6.2753 6.2732 Space group and cell parame- 3 20.51710120.514 0.0034 29.6 4.3253 4.3260 ters see text. (Observed (obs) 4 22.947 ? 1.8 3.8725 and calculated (calc) values, d- 5 24.56311024.559 0.0033 75.1 3.6213 3.6218 spacing values, I refers to inte- 6 28.42920028.433 −0.0037 4.8 3.1370 3.1366 grated intensities scaled in per- 7 29.89300229.891 0.0021 9.1 2.9866 2.9868 centage of the strongest reflec- 8 30.458 ? 1.7 2.9325 tion No. 11. Asterisks (*) indi- *9 30.89910130.881 0.0180 2.2 2.8916 2.8933 cate the reflections assigned to 10 31.514 ? 1.3 2.8366 2H-TaSe2, zero point (refined): 11 32.20520132.208 −0.0035 100.0 2.7773 2.7770 for H-TlTaSe3 z = 0.0178, for 12 32.768 ? 4.4 2.7308 2H-TaSe2 z = −0.0391). 13 33.19210233.196 −0.0027 24.6 2.6969 2.6967 *14 33.22310233.258 −0.0351 19.9 2.6945 2.6917 15 35.517 ? 1.2 2.5255 16 36.225 ? 9.9 2.4778 *17 36.89610336.919 −0.0223 1.4 2.4342 2.4328 18 37.92221037.917 0.0057 12.2 2.3707 2.3710 19 40.92421140.918 0.0065 5.3 2.2034 2.2038 20 41.71220241.725 −0.0132 121.4 2.1636 2.1630 21 43.24130043.231 0.0094 12.8 2.0906 2.0911 22 46.679 ? 5.8 1.94443 23 49.01721249.014 0.0029 8.9 1.8569 1.8570 24 50.34622050.348 −0.0019 24.9 1.8110 1.8109 25 52.55231052.557 −0.0051 7.3 1.7400 1.7399 *26 53.37211053.364 0.0080 3.1 1.7152 1.7155 27 54.190 ? 2.6 1.6912 28 54.55220354.545 0.0073 5.0 1.6809 1.6811 *29 55.44311255.433 0.0100 1.5 1.6559 1.6562 30 57.553 ? 0.8 1.6001 *31 57.99500857.992 0.0026 3.1 1.5890 1.5891 32 59.65722259.662 −0.0056 4.6 1.5486 1.5485 dle of the heating zone while the other end reached just out- side the furnace tube. While keeping the temperature of the mixture just above the melting point of TlBr (480 ◦C), TlBr sublimated to the cooler zone of the glass ampoule. After about three days all TlBr had separated from the mixture leaving behind bunches of slim black shiny crystal needles of TlTaSe3 (Fig. 1). The length L of the needles was in the range of 100 µm ≤ L ≤ 2 mm. Some of these crystals could be isolated and were suitable for single crystal X-ray struc- ture investigations and also for electrical resistivity measure- ments. An EDX analysis indicated the presence of the three elements Tl, Ta and Se with an approximate atomic ratio of 1:1:3, and no bromine was detected. Characterisation Fig. 1. SEM micrograph of O-TlTaSe3 crystals as grown X-ray investigations from a TlBr melt (s. text). X-Ray powder diffraction was carried out on a SIEMENS lar ratio 1:1) was filled into in a glass (DURAN R ) ampoule D5000 diffractometer in the range of 7◦ ≤ 2θ ≤ 60◦ using λ = . ˚ (ca. 18 cm long). After rinsing with dry argon and evacu- Cu-Kα1 ( 1 54056 A) radiation. Surprisingly, the powder ation (p ≈ 8 mbar) it was flame-sealed and placed asym- patterns of the black bulk and that of the crystal needles from metrically inside the tube of a horizontally arranged furnace. the TlBr melt were not identical. The latter resembles that The one end of it with the mixture was located in the mid- of the homologous sulphide TlTaS3 with orthorhombic sym- 860 C. L. Teske et al. · Preparation, Crystal Structure, Properties, and Electronic Band Structure of TlTaSe3 Table 2. Crystal data and structure refinement for Table 4. Anisotropic displacement parameters (A˚ 2) for c O-TlTaSe3 . O-TlTaSe3. The anisotropic displacement factor exponent 2 2 ∗2 ∗ ∗ Empirical formula TlTaSe3 takes the form: −2π [h a U11 + ...+ 2hka b U12], U12 = Formula weight 622.20 U23 = 0. Temperature 293(2) K Atom U U U U ˚ 11 22 33 13 Wavelength 0.71073 A Tl 0.036(1) 0.030(1) 0.049(1) 0.002(1) Crystal system orthorhombic Ta 0.019(1) 0.026(1) 0.030(1) −0.002(1) Space group Pnma Se(1) 0.018(1) 0.019(1) 0.033(1) 0.003(1) = . ( ) ˚ Unit cell dimensions a 9 5540 13 A Se(2) 0.024(1) 0.026(1) 0.030(1) −0.003(1) = . ( ) ˚ b 3 6244 6 A Se(3) 0.016(1) 0.019(1) 0.031(1) 0.000(1) c = 14.7271(17) A˚ Volume 509.96(12) A˚ 3 Z 4 Table 5. Selected interatomic distances (A)˚ for O-TlTaSe3 Density (calculated) 8.10 g/cm3 based on the single crystal data. Estimated standard devia- Absorption coefficient µ 74.2 mm−1 tions are given in parentheses. F(000) 1024 Tl Se1 3.191(2) 1× Se1 Ta 2.5765(13) 2× Crystal size 0.3 × 0.1 × 0.1mm3 × × ◦ ◦ Se2 3.1965(17) 2 Tl 3.191(2) 1 θ-Range for data collection 2.54 – 30.01 Se2 3.2998(17) 2× Tl 3.4526(17) 2× − ≤ ≤ Index ranges 13 h 1, Se3 3.393(2) 1× Se2 Ta 2.3799(19) 1× −5 ≤ k ≤ 5, Se1 3.4526(17) 2× Tl 3.1965(17) 2× −1 ≤ l ≤ 20 Tl 3.6244(6) 2× Tl 3.2998(17) 2× Reflections collected 1764 Ta Se2 2.3799(19) 1× Se3 Ta 2.6066(12) 2× Independent reflections 852 [R(int) = 0.1085] Se1 2.5765(13) 2× Ta 2.8193(19) 1× Completeness to θ = 30.01 100.0% Se3 2.6066(12) 2× Tl 3.393(2) 1× 2 Refinement method Full-matrix least-squares on F Se3 2.8193(19) 1× Min./max.
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