Neo-isotype
Gemstone like compounds with same structure but different composition.
Only accessible via mechanosynthesis/mechanochemistry.
They could be called non statistic solid solutions or deterministic solid solutions.
Subset of regularly patterned substitutions could be called: "checkerboard compounds".
Examples
See: pseudo phase diagrams for more details on this.
The rutile stishovite (TiO2 to strong SiO2) neoisotypic 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) neoisotypic 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 neoisotypic 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 neoisotypic 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 neoisotypic 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 neoisotypic transition
Pure AlN hydrolyzes with water, so when going far with the forced substitutuion the parts must be perfectly sealed against humidity.
- The tistarite to leukosapphire to diboron trioxide (Ti2O3 to Al2O3 to B2O3) neoisotypic 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.
Examples with likely missing end members
Take gem grade silicon carbide aka moissanite as starting point.
Then increasinvgly substitute the silicon Si atoms with titanium Ti atoms in a checkerboard fashion.
It is known that pure TiC likes to be in simple cubic rock salt structure, so at some degree of substitution.
the structure might become weakly metastable (worst case explosive) or entirely unstable.
Revesely, staring with simple cubic rock salt structure TiC and
substituting Ti with Si (or Ge) in checkerboard fashion seem more limited if possible at all.
Titanium carbide MXenes Ti2C1, Ti3C2, Ti4C3(?)
Might be checkerboard pattern Si/Ge substitutable by some degree.
Due to todays experimental syntehsis route via MAX phases and etching out A,
it is likely unclear in how far titanium carbide MXenescan be extended from
2D materials to a 3D materials that in the limit have Ti1C1 stoichometry.
That is: In how far they are metastable to transformation to
the known to be low energy stable simple cubic rock salt structure polymorph of TiC.
Side-note: MXenes have dense fcc==ccp structure akin to many metals.
Unlike moissanite and dioamondoids in general which are sparse,
half the atomic coordination, and voids due to being two interspersed fcc lattices.
Related
- Pseudo phase diagram - mapping out neo-polymorphs & neo-isotypes
Examples:
- Cook mix and stir thermodynamic synthesis - conventional constraint
External links
- https://en.wikipedia.org/wiki/Isomorphism_(crystallography) - conventional isotypes
- https://en.wikipedia.org/wiki/Solid_solution - conventional constraint