A neo-polymorphic compound (or neo-isomorphic compound) is a highly stable non equilibrium polymorph of a material with a certain fixed stoichiometry that is exclusively accessible through mechanosynthesis.
This includes patterns where specifically ordered states are thermodynamically not more attractive than disordered (or in other undesired form ordered) states but where a (sufficiently) high activation energy lies between the ordered and unordered states.
The patterns can be:
- different atom types (elements) ... specific example: A crossover gemstone between Rutile (polymorph of TiO2) and Stishovite (polymorph of SiO2). The pattern making elements are Ti & Si. Oxygen atoms stay at their places.
- different stacking geometry or ... specific example: A crossover between Diamond (cubic stacking) and Lonsdaleite (hexagonal stacking). (When pointing up a tetrapod of carbon bonds there are two ways one can orient the up facing three bonds in a six direction hexagon).
- ABABBABBBBAABABAABAA – unwanted unordered state – may be the only one that is thermodynamically accessible
- ABABABABABABABABABAB – unwanted ordered state – may be the only one that is thermodynamically accessible
- AABBAABBAABBAABBAABB – neo-polymorph – wanted peculiarly ordered state – not thermodynamically accessible - but accessible via mechanosynthesis
Of course arbitrary many elements/layertypes/... are allowed. A,B,C,D,...
Note: Thermodynamic accessibility refers to all the crude processes available today (2017) that only allow to handle matter in statistical quantities: melting, mixing, cooling, pressurizing, irradiating, ... This explicitly excludes advanced mechanosynthesis.