Chemischer Transport fester Lösungen. 15 [1]. Der Chemische Transport von Mischphasen in Systemen TiS₂/TiSe₂, TiS₂/TaS₂, TiSe₂/TaSe₂ und TaS₂/TaSe₂

Abstract

Röntgenographische Untersuchungen haben gezeigt, dass in den Systemen TiS2/TiSe2, TaS2/TaSe2, TiS2/TaS2 und TiSe2/TaSe2 lückenlose Mischkristallreihen gebildet werden. Die Gitterkonstanten der Mischphasen folgen im Wesentlichen der Vegardschen Regel. Erfolgt die Substitution im Anionenteilgitter (TiS2/TiSe2, TaS2/TaSe2) sind die Gitterkostanten a der Mischphasen fast stets kleiner, c hingegen größer als nach der Vegardschen Regel zu erwarten.Mithilfe Chemischer Transportreaktionen (Transportmittel Iod, 1000 → 900 °C) können die genannten Mischphasen in einkristalliner Form erhalten werden. Für die Systeme TiS2/I2 und TiSe2/I2 wurden orientierende thermochemische Modellrechnungen durchgeführt. Titan(IV)‐iodid erweist sich danach als die transportwirksame Gasphasenspezies. Der Transport verläuft in allen vier Systemen annähernd kongruent.

Improved chemical vapor transport growth of transition metal dichalcogenides

“…The other salts of ammonium led rather to powders instead of crystals, the smallest grains being observed when using ammonium chloride. The growth process passes through an initial reaction between titanium and the halogen that produces many volatile halides, above all TiX 4 [10,11]. For the formation of these molecular species from the ammonium salts, the preliminary step of thermal decomposition is necessary: NH 4 Y → NH 3 + HY (Y = halogen element).…”

Forcing substitution of tantalum by copper in 1T-TaS2: synthesis, structure and electronic properties of 1T-Cu x Ta1−x S2

“…Divalent metals should be soluble in 1T-TaS 2 up to x = 0.33, which is found for the divalent iron and cobalt [27]. Tetravalent metals should be fully miscible in 1T-TaS 2 as found for the group 4 metal titanium [23,28]. The reduction of the conduction electron number by doping 1T-TaS 2 with monovalent copper therefore holds as an explanation for the c-lattice parameter variation that references to a maximum homogeneity range of 1T-Cu 0.25 Ta 0.75 S 2 .…”

“…Substantial efforts were made to investigate doped systems of the type 1T-M x Ta 1−x S 2 . As a result, experimental data are available today for the systems with the following metals M: Ti, Zr, Hf, Nb, V, Cr, Mn, Fe, Co and Ni [13,[23][24][25][26][27][28]. Interestingly, information about doping 1T-TaS 2 with coinage metals is missing.…”

Preparation and Crystal Growth of Transition Metal Dichalcogenides

“…Ta 1-x M x Ch 2 mixed phases (M: Ti, Mo, Nb, Ch: S, Se): (a) [34,38,39] On (a): Like the binary compounds, mixed phases in crystalline form in which Ta atoms are substituted by Ti, Nb, or Mo atoms can be produced by endothermic chemical transport with iodine.…”

“…[89] On (e): A relatively unusual route to TaTe 2 crystals is the thermal decomposition of NiTaTe 5 [90] obtained by chemical transport. [91] TaCh 2 mixed phases (Ch: S, Se): (a) [34,[92][93][94][95][96] On (a): The interest in mixed phases TaS x Se 2-x is related to an unusual physical property of these compounds: Charge density waves and superconductivity are observed simultaneously. [93,94] For the same reason, a phase of the composition Ta 1-x Fe x SSe was investigated and described.…”