What is 1111 phase in material science

[Shriphysics]

Hi Guys,
I wonder if someone tells me about what are the rules for nomenclature of phases in materials.
Generally I read like 1111 phase, 122 family, 11 system. I don't understand completely about this. Does they talk about composition or something else?
for ex.- BaFe2As2 is 122 phase material, LaFeAsO is 1111 family compound.
Kindly guide me in any related context.

Thanks in advance.
Shriphysics

[Mapes]

Hi, Shriphysics, welcome to PF. Looks like just the relative molar amounts of each component, no? That is, LaFeAsO is 1111 because it's La1Fe1As1O1.

[Shriphysics]

Hi Mapes,
Thanks for reply...I was also thinking same but wanted to confirm from someone.
Anyway now I wonder if you know FeTe is 11 phase no problems about it, but when we prepare a composite Fe(1)Se(0.5)Te(0.5) then also we say it as 11 phase, why its not like 1 1/2 1/2 phase??

[Mapes]

I haven't worked with this particular material, but my best guess is that FeX is a binary compound between iron and X, and that selenium can substitute for tellurium in the crystal structure. From a crystal structure standpoint, therefore, things don't change much for FeTexSe1-x as x varies from 1 to 0. But this is just my speculation.