e.g. the difference between AlxGa1-xAs (ternary alloy) and (AlAs)x(GaAs)1-x (solid solution)?
- From thermodynamic point of view?
- From crystallographic point of view ?
- From growth process point of view?
- From growth technique point of view?
- From crystal quality point of view?
Dear all,
Both writing: AlxGa1-xAs and (AlAs)x(GaAs)1-x define exactly the same composition ranges from AlAs to GaAs (the amount of As is fixed to 50% at.).
On the thermodynamic point of view this section describes the pseudo-binary phase diagram AlAs-GaAs. Nevertheless, the composition of the phases formed are not obliged to be on this "virtual" phase diagram if the tielines (equipotential lines) do not lie in the section.
As a function of temperature and composition, and at equilibrium, the alloy may be formed of 1, 2 or 3 phases (never more in a ternary due to Gibbs rule). These phases can be solid solution with substitutions in the same lattice structure as the elements or intermetallics with completely different crystal structures.
Regards
The boundaries are a bit floating. Solid solutions might be the more general category, where alloys can be more specific related to crystalline micro-structure, where some inter-metallic phases have specific stoichiometry and crystal structure, see also https://en.wikipedia.org/wiki/Alloy
Steffen Berg
Thank you very much for your answer.
I need some references a bit more specialized than wiki.
Dear all,
Both writing: AlxGa1-xAs and (AlAs)x(GaAs)1-x define exactly the same composition ranges from AlAs to GaAs (the amount of As is fixed to 50% at.).
On the thermodynamic point of view this section describes the pseudo-binary phase diagram AlAs-GaAs. Nevertheless, the composition of the phases formed are not obliged to be on this "virtual" phase diagram if the tielines (equipotential lines) do not lie in the section.
As a function of temperature and composition, and at equilibrium, the alloy may be formed of 1, 2 or 3 phases (never more in a ternary due to Gibbs rule). These phases can be solid solution with substitutions in the same lattice structure as the elements or intermetallics with completely different crystal structures.
Regards
Dear Dr Gossé Stéphane
Thank you very much for your sound and concise explanation.
Best regards,
Professor A. Kadri
Dear all, If i may add my basic understanding. Solid solution is an ability of an atom to penetrate and find his place in a crystal lattice. All substances that we have on Earth are, basically, solid solutions because we can never get rid of impurities. Solid solution can be used to change the properties that we need. It can achieved by diffusion without melting (long time). Diffusion accelerates mutual penetration with heat nearly 0.5 - 0.7 of melting T. That is how we achieve reasonable level of penetration in thin surface layers (the diffusion welding was developed in USSR in 1953). Environmental corrosion is a good example of solid solutions formation, but this is not an alloy. And the process is not uniform as it goes mostly near the surface. Diffusion is faster in liquids, larger volumes can be mixed. That is why we need alloying. It goes via liquefaction. Alloy is a result of liquefaction, mixing and solidification of some chemical elements together. A uniform crystal or several phases with limited possible concentrations are formed (as already mentioned above) - each of the new alloy component can be referred to as a solid solution.
With best regards
Dear Anton Pshenichnikov ,
Thank you very much for your thorough and elegant explanation,
Best regards,
Professor A. Kadri
In general cases of solid solution the atoms are arranged in random fashion on the atomic sites, alloy is a particular case of solid solution so "alloy = solid solution with metallic proprieties composed of more than 1 element" where the atoms must be arranged in regular fashion on the atomic sites this regular arrangement appear when the valencies/elecro-negativity of the atoms are nearly the same, and the size difference between the atoms are less than 20%.
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials
- Inorganic Materials
- Metals
- Alloys