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I am currently reworking our condensed matter lecture. We shortly discussed topologic insulaters at the example of

$$\text{Bi}_{1-x}\text{Sb}_{x}$$

I am not sure what the $x$ stands for. Normally the index at an element tells me "how many atoms of that element there are", but in this case we are discussing values of $x = 0.04$ etc. so this does not make sense. I read through some papers but could not find any explanation.

Any idea of what x could mean is appreciated.

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Normally the index at an element tells me "how many atoms of that element there are", but in this case we are discussing values of $x = 0.04$ etc. so this does not make sense.

That is still what it means. You just need to beat it with a rubber hammer until it starts making sense.

In this particular instance, for example, it means that four atoms out of every 100 are tin, and the rest are bismuth.

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  • $\begingroup$ Thanks! Made my day xD $\endgroup$
    – Tera
    Commented Jan 8, 2020 at 15:20
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If 100% of the medium is composed of the two elements $A$ and $B$, than a easy ways to write the percentages $p_A$ and $$x=p_B=1-p_A$$ is $A_{p_A}B_{p_B}$. Thus, in your case it becomes $A_{1-x}B_x$.

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  • $\begingroup$ Thanks for that quick and helpful answere! $\endgroup$
    – Tera
    Commented Jan 8, 2020 at 15:18

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