Croissance en solution à haute température de monocristaux de phases MAX

par Damir Pinek

Projet de thèse en 2MGE : Matériaux, Mécanique, Génie civil, Electrochimie

Sous la direction de Thierry Ouisse.


  • Résumé

    The general formula of MAX phases is Mn+1AXn, where M is a transition metal, A is an element of groups 13 to 16, and X is either carbon or nitrogen (see, e.g., Fig.1). MAX phases are nanolamellar compounds, which combine the good properties of metals (large electrical conductivity) to those of ceramics (high resistance to thermal shocks and extreme temperatures, chemical stability). These properties make them potentially attractive for applications such as heating elements, non-oxidizing electrical contacts, rotating parts or reactor turbines, supercapacitors, nuclear cladding, etc. Until recently, the difficulty to produce single crystal MAX phases prohibited a thorough investigation of their physical properties. Three years ago, the LMGP team found the way to produce such single crystals, and this opened the door to new lines of research in a field which already triggers an intense international research activity [1-5]. One of the new emergent aspects in the field is the development of a new class of two-dimensional (“graphene-like”) objects called MX-enes, by dissociation of the weaker A planes [6]. For some applications, these new 2D systems clearly require the use of single crystals. The project deals with the synthesis of new types of single-crystalline MAX phases and the characterization of their structural properties. The crystals will be synthesized at LMGP (Grenoble) by using the high temperature solution growth reactors already developed at the lab [1-6]. The applicant will study nucleation and growth phenomena (thermodynamics, kinetics, etc.) for different MAX phases (obtained by changing the M and A atoms). Many of the physical properties will then be assessed through collaborations conducted within the frame of a National program supported by the French National Research Agency (ANR). The PhD work is focused on the crystal growth aspects, and is aimed at fulfilling two objectives: First, to produce various single crystals with areas around 1cm2 by spontaneous nucleation in the solution, and secondly, to use those crystals as seeds to develop Top Seeded Solution Growth (TSSG). The second objective is rendered necessary by the fact that for many MAX phases, it is quite difficult to separate the as-grown crystals from the solidified flux due to a lack of chemical selectivity, a problem which does not exist in the case of TSSG. In addition, it is the only way to increase the final size of the platelet and to completely control the supersaturation and crystal growth, so as to avoid unwanted parasitic nucleation. The applicant will also have to determine the best growth conditions, based upon the knowledge of the ternary phase diagrams if they exist, or upon reasonable guesses from the known binary phase diagrams related to the envisioned MAX phases. Within the frame of the project, the crystals will be put to good use by the scientific partners for producing original two-dimensional MX-ene nanocrystals from the three-dimensional crystals. As an example, two-dimensional nano-crystals of Ti3C2 (MX-ene) have already been obtained by others through a selective etching of the Al layers of Ti3AlC2 nanocrystals [7]. Equipment, travels and consumables will be first funded by the French ANR, and are part of a 42 months national project entitled MAXICRYST, which started in april 2014. Additional fundings should come from European projects to be submitted in 2016.

  • Titre traduit

    High Temperature Solution Growth of Single Crystals of MAX phases


  • Résumé

    The general formula of MAX phases is Mn+1AXn, where M is a transition metal, A is an element of groups 13 to 16, and X is either carbon or nitrogen (see, e.g., Fig.1). MAX phases are nanolamellar compounds, which combine the good properties of metals (large electrical conductivity) to those of ceramics (high resistance to thermal shocks and extreme temperatures, chemical stability). These properties make them potentially attractive for applications such as heating elements, non-oxidizing electrical contacts, rotating parts or reactor turbines, supercapacitors, nuclear cladding, etc. Until recently, the difficulty to produce single crystal MAX phases prohibited a thorough investigation of their physical properties. Three years ago, the LMGP team found the way to produce such single crystals, and this opened the door to new lines of research in a field which already triggers an intense international research activity [1-5]. One of the new emergent aspects in the field is the development of a new class of two-dimensional (“graphene-like”) objects called MX-enes, by dissociation of the weaker A planes [6]. For some applications, these new 2D systems clearly require the use of single crystals. The project deals with the synthesis of new types of single-crystalline MAX phases and the characterization of their structural properties. The crystals will be synthesized at LMGP (Grenoble) by using the high temperature solution growth reactors already developed at the lab [1-6]. The applicant will study nucleation and growth phenomena (thermodynamics, kinetics, etc.) for different MAX phases (obtained by changing the M and A atoms). Many of the physical properties will then be assessed through collaborations conducted within the frame of a National program supported by the French National Research Agency (ANR). The PhD work is focused on the crystal growth aspects, and is aimed at fulfilling two objectives: First, to produce various single crystals with areas around 1cm2 by spontaneous nucleation in the solution, and secondly, to use those crystals as seeds to develop Top Seeded Solution Growth (TSSG). The second objective is rendered necessary by the fact that for many MAX phases, it is quite difficult to separate the as-grown crystals from the solidified flux due to a lack of chemical selectivity, a problem which does not exist in the case of TSSG. In addition, it is the only way to increase the final size of the platelet and to completely control the supersaturation and crystal growth, so as to avoid unwanted parasitic nucleation. The applicant will also have to determine the best growth conditions, based upon the knowledge of the ternary phase diagrams if they exist, or upon reasonable guesses from the known binary phase diagrams related to the envisioned MAX phases. Within the frame of the project, the crystals will be put to good use by the scientific partners for producing original two-dimensional MX-ene nanocrystals from the three-dimensional crystals. As an example, two-dimensional nano-crystals of Ti3C2 (MX-ene) have already been obtained by others through a selective etching of the Al layers of Ti3AlC2 nanocrystals [7]. Equipment, travels and consumables will be first funded by the French ANR, and are part of a 42 months national project entitled MAXICRYST, which started in april 2014. Additional fundings should come from European projects to be submitted in 2016.