No. Depends on your definition of rare, of course. You can see prices for various formulations and purities if you Google. Strontium titanate is used for jewelr

No. Depends on your definition of rare, of course. You can see prices for various formulations and purities if you Google. Strontium titanate is used for jewelry, as it was one of the main diamond simulants back before cubic zirconia. I did my PhD working with crystals of strontium titanate and contributed to two Wikipedia articles on it. Looking at the elemental abundances you can see that titanium and strontium are fairly high, above both gallium and arsenic, another solar cell pair. Barium is in the ballpark of gallium and arsenic. https://en.m.wikipedia.org/wiki/Abundance_of_the_chemical_elements https://en.m.wikipedia.org/wiki/Abundance_of_the_chemical_el...