Neo-polymorph

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).
• ...

Patterns:

• 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 (2020) that only allow to handle matter in statistical quantities: melting, mixing, cooling, pressurizing, irradiating, ... This explicitly excludes advanced mechanosynthesis.

Examples

See: pseudo phase diagrams for more details on this.

The rutile stishovite (TiO₂ to strong SiO₂) neopolymorphic transition:
The common mineral rutile and the rare mineral stishovite (made out of the two most common elements in earth crust) share the same crystal structure. The rutile structure. Albeit rutile not drawing silicon into its structure naturally (meaning it's thermodynamically unfavourable) (as can be seen with rutile occuring embedded in quartz https://commons.wikimedia.org/wiki/File:Rutile@quartz.jpg) a forced substitution (at least to some degree) may very well be possible via mechanosyntheic means and the resulting product base material may very well be highly (meta) stable at room temperature.

The quartz to "carbexplosoquartz" (SiO₂ to solid CO₂) neopolymorphic transition
Obviously CO₂ very much likes to be a gas (small atomic radii => sp orbitals sticking far out => orbitals hybridize and form double bonds) so if pure CO is even mechanosynthsizable it would be a very delicate and thus dangerous high explosive. A little bit of substitution of Si with C may be safely forcable via mechanosynthetic means though, despite that substitution is not naturally happening due to unvafourable thermodynamics. Maybe even as much as 50% of the silicon could be substituted with carbon without getting to something unstable and useless? Who knows.

The SiO₂ to GeO₂ and SnO₂ neopolymorphic transition
Si has a bit more dissimilarity to the element above (C) than the elements below (Ge,Sn) with the exception of (Pb). Like less relative difference in diameter, less difference in their dislike to form double bonds, less difference in their metallicity, ... . So these elements may be substitutable in higher quantities. Though Ge and Sn are to rare to be of use as large volume structural base material. Also Ge and Sn form rutile structure (argutite and cassiereite respectively), so they may instead be able to tie into the aforementioned rutile stishovite neopolymorphic transition. Lead (Pb) may very well already be way too different to Si to even be force substitutable making the resulting structures unstable at room temperature or even below. Lead and tin are (and where) used in the floating glass production process because they don't like to mix too much (on their own volition). Still a lot of unwettability and immiscibility may be possible to overcome via mechanosynthetic forcing. Also there is lead glass (Template:TODO)

• The Si₃N₄ to beta carbon nitride C₃N₄ neopolymorphic transition
  

Both are high performance materials but beta carbon nitride is highly exotic even in its pure form today (2020). Beta carbon nitride may be of especial interest since when drawing solid building material form thin air alone The concentration of CO₂ is the limiting factor and given more than halve of C₃N₄ is nitrogen and thus material may be drawable more than double the speed.

• The BN to AlN neopolymorphic transition
  

Pure AlN hydrolyzes with water, so when going far with the forced substitutuion the parts must be perfectly sealed against humidity.

• The leukosapphire to diboron trioxide (Al₂O₃ to B₂O₃) neopolymorphic transition
  

Pure B₂O₃ is slightly water soluble and toxic, so when going far with the forced substitutuion the parts must be perfectly sealed against humidity.

Related

• pseudo phase diagram - mapping out neo-polymorphs
• Simple crystal structures of especial interest - browse there as a starting point

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• diamondoid compound
• binary diamondoid compound

External links

Wikipedia pages:

• Polymorphism (materials science)
• Polymorphs of silicon carbide
• isomer, stereoisomer, conformational isomer
• Superstructure (condensed matter)
• Isomorphism_(crystallography)

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• Isotype: (de) Translated citation: "Minerals of the same structural type are called isotypes. They crystallize in the same class of crystals and form similar crystal forms. "
• Isotype: (wikipedia de) Isotyp

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• www.mineralienatlas.de
  lists minerals with equal or similar structures for any given mineral
  so thhis can serve as a possible starting point to find potential neo-polymorphs