Layered transition metal chalcogenides, MX₂ (X = S, Se or Te) are long known and include a variety of compounds with a wide spectrum of electronic properties (semiconducting, semimetals, superconductivity and charge ordering). Recent studies on exfoliated semiconducting MoS₂ mono-layers have roused a growing interest in this class of materials, as being promising candidates for novel electronics, complementary to graphene. Tunability of the electronic structure in TiSe₂ and superconducting Cu-intercalated TiSe₂ has motivated investigations on the interplay between superconductivity and charge ordering. Despite of long standing reports on the crystal growth of MX₂ and wide growing interest in this materials, many details of the growth process (in most of the case, the crystals are prepared by Chemical Vapour Transport, CVT) and optimum experimental conditions still remain overlooked. In this work, we report the results of a systematic investigation of the effects of various parameters, like temperature, thermal gradient, nominal composition, total pressure, concentration of the transport agent and its nature, and annealing time on the crystal growth of semi-metallic TiSe₂, superconducting Cu_xTiSe₂ and semiconducting TaX₂ and MoX₂ (X = S, Se, Te). By optimizing the temperature, the temperature gradient and the initial concentration of I₂, very large crystals of about 1 cm² were grown within one day, instead of several days as usually reported. The effect of the I₂-M ratio has been better clarified, highlighting that the transport and growth mechanism occur via the formation of highly volatile iodides, like TiI₄, that determines the nucleation rate. The growth kinetic is very fast at the beginning of the process and, depending on the temperature, mm² sized crystals can grow in few hours. Copper intercalated crystals could be grown either directly from a mixture of Cu, Ti, Se, using iodine, or by intercalating Cu atoms in already grown TiSe₂ crystals. In both cases, the copper content can be controlled and superconducting crystals are obtained. The effects of the nominal starting composition, in additions to the others factors, is discussed Interestingly, iodine is proven not to be the most effective transport agent for the heavy transition metals, like Mo and Ta. For this reason, a new growth route, starting from mixtures of chlorides, MoCl₃, MoCl₅ or TaCl₅, and their metals, was successfully gone through. In this case, the upper temperature was found to be the most critical parameter must be tuned as a function of the chalcogen element. The morphology of the crystals depends on the starting chlorine concentration and whiskers of TaSe₂ as thin as few µm and several mm long were found to grow when the Cl/Ta is too high.

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