  Two-dimensional (2D) materials and Transition Metal Dichalcogenides (TMD) in
particular are at the forefront of nanotechnology. To tailor properties for
engineering applications, alloying strategies used for bulk metals in the last
century need to be extended to this novel class of materials. Here we present a
systematic analysis of the phase behaviour of substitutional 2D alloys in the
TMD family on both the metal and chalcogenide site. The phase behaviour is
quantified in terms of a metastability metric and benchmarked against
systematic computational screening of configurational energy landscapes. The
resulting Pettifor maps can be used to identify broad trends across chemical
spaces and as starting point for setting up rational search strategies in phase
space, thus allowing for targeted computational analysis of properties on
likely thermodynamically stable compounds. The results presented here also
constitute a useful guideline for synthesis of binary metal 2D TMDs alloys via
a range of synthesis techniques.
