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I am collecting a database of perovskite materials and could not decide if $\ce{LiNbO3}$ is categorized as perovskite or not. $\ce{LiNbO3}$ has been identified as a perovskite [1] as well as non-perovskite [2 , appendix] in literature. Which is correct? Usually the structure type of some compounds are written as ($\ce{LiNbO3}$-type or LN-type), are these perovskites or not?

Relevant publications are also appreciated.

EDIT:

Goldschmidt tolerance factor of $\ce{LiNbO3}$: 0.748 (should appr. be between 0.8 and 1.1 to be perovskite)

Tau factor of $\ce{LiNbO3}$(as proposed here): 8.678 (should be less than 4.18 to be perovskite. Tau factor is proven to be more accurate than tolerance factor)

These tolerance factors indicate $\ce{LiNbO3}$ should be non-perovskite, however, I found some other materials such as $\ce{BiSrCr2O6}$ that pass tolerance factor tests but still form LN-type structure. This is where the confusion comes :(

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  • $\begingroup$ 2 doesn't specifically say that it is a non perovskite $\endgroup$
    – pjmathematician
    Commented Jun 11, 2020 at 13:57
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    $\begingroup$ It may have several different known phases... $\endgroup$
    – Greg
    Commented Jun 11, 2020 at 13:57
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    $\begingroup$ @Pj30 They have reported a database of perovskites and non-perovskites, as you would find here(advances.sciencemag.org/highwire/filestream/210992/…). In this database LiNbO3 was categorized as non-perovskite. $\endgroup$
    – Achintha Ihalage
    Commented Jun 11, 2020 at 14:00
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    $\begingroup$ @AchinthaIhalage got it $\endgroup$
    – pjmathematician
    Commented Jun 11, 2020 at 14:05
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    $\begingroup$ I guess the real question is how distorted from real Perovskite (the actual mineral) is still a perovskite (general name for similar materials). Orthorhombic and tetragonal at least maintain right angles, trigonal is a distortion along the body diagonal so the sides are no longer rectilinear. What is 'correct'? Strictly speaking, only a true cubic material is Perovskite-like. $\endgroup$
    – Jon Custer
    Commented Jun 11, 2020 at 21:20

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LiNbO3 has quite a unique non-perovskite structure (under ambient conditions) and it's referred to as a structural type (LiNbO3-type structure) as a result (see here). This is largely due to Li+ being a very small cation.

The tolerance factor from Victor Goldschmidt is a classifier with moderate accuracy, so it's not surprising that even if a material passes its test, it may still not acquire a perovskite structure.

The other (hidden) assumption that may cause confusion is that these classifiers for perovskite structures are usually trained for conditions at ambient temperature and pressure. So they can fail badly if this condition is no longer valid because a material can be in a non-perovskite phase under ambient conditions, but in the perovskite phase under some other conditions.

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