Neo-polymorph: Difference between revisions

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{{wikitodo|There is a significant mixup with '''neo-isotypes''' here. Move relevant parts to the new page.}}
{{wikitodo|There was a significant mixup with '''neo-isotypes''' here. Do some more cleanup & checks if transition succeeded.}}
{{site specific term}}
{{site specific term}}


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'''Examples:'''
'''Examples:'''
* [[Dialondeite]]
* [[Dialondeite]]
== Examples with likely missing end members ==
Take gem grade silicon carbide aka [[moissanite]] as starting point. <br>
Then increasinvgly substitute the silicon Si atoms with titanium Ti atoms in a checkerboard fashion. <br>
It is known that pure TiC likes to be in simple cubic rock salt structure, so at some degree of substitution. <br>
the structure might become weakly metastable (worst case explosive) or entirely unstable. <br>
Revesely, staring with simple cubic rock salt structure TiC and <br>
substituting Ti with Si (or Ge) in checkerboard fashion seem more limited if possible at all. <br>
Titanium carbide MXenes Ti<sub>2</sub>C<sub>1</sub>, Ti<sub>3</sub>C<sub>2</sub>, Ti<sub>4</sub>C<sub>3</sub>(?) <br>
Might be checkerboard pattern Si/Ge substitutable by some degree. <br>
Due to todays experimental syntehsis route via MAX phases and etching out A, <br>
it is likely unclear in how far titanium carbide MXenescan be extended from <br>
2D materials to a 3D materials that in the limit have Ti<sub>1</sub>C<sub>1</sub> stoichometry. <br>
That is: In how far they are metastable to transformation to <br>
the known to be low energy stable simple cubic rock salt structure polymorph of TiC. <br>
Side-note: MXenes have dense fcc==ccp structure akin to many metals. <br>
Unlike [[moissanite]] and dioamondoids in general which are sparse, <br>
half the atomic coordination, and voids due to being two interspersed fcc lattices. <br>


== External links ==
== External links ==

Revision as of 12:03, 26 September 2025

(wiki-TODO: There was a significant mixup with neo-isotypes here. Do some more cleanup & checks if transition succeeded.)

This article defines a novel term (that is hopefully sensibly chosen). The term is introduced to make a concept more concrete and understand its interrelationship with other topics related to atomically precise manufacturing. For details go to the page: Neologism.


A neo-polymorphic compound (or neo-isomorphic compound) is a highly (meta)stable non equilibrium polymorph
of a material with a certain fixed stoichiometry that is exclusively accessible through mechanosynthesis.
If just one element is involved the term neo-allotrope can be applied too/instead.

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
making the via conventional means inacessible states highly kinetically metastable.

The patterns can be:

  • different stacking geometry, 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).
  • changes between different crystal structures of the same composition (adn stoichometry) so long nigh seamless covalent transitions are possible

Excluded here:

  • changes of atom types and stoichometry falls under neo-isotypes instead:
    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.

Stacking order 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
  • ABBAABBAABBAABBAABB – neo-polymorph – wanted peculiarly ordered state – not thermodynamically accessible - but accessible via mechanosynthesis

Note: in the case of SiC (moissanite) there is the constraint of no two same letters following adjacently. Above examples for simplicity.

Also neo-polymorphs and neo-isotypes can intermix here to neo gemstones like compounds or neo-gems for short.
All sorts of II-IV semiconductor compounds have fitting structure stacking order variations in {111} directions.
So structural stacking order can be augmented with material type stacking order.
Material stacking order not being constrained to the by {111} directions but by lattice strain.

Note: Thermodynamic accessibility refers to all the crude processes available today (2025)
that only allow to handle matter in statistical quantities: <br< melting, mixing, cooling, pressurizing, irradiating, (cook mix and stir thermodynamic synthesis) ...
This explicitly excludes advanced mechanosynthesis.

Examples

See: pseudo phase diagrams for more details on this.


Related

Examples:

External links

Wikipedia pages:

  • 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
  • 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
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