GATE 2024 CY – Question 22

Inorganic Chemistry · Solids: Crystal systems and lattices, Miller planes, crystal packing, crystal defects, Bragg’s law, ionic crystals, structure of AX, AX2, ABX3 type compounds, spinels, band theory, metals and semiconductors, Zeolites and their applications. · 1 mark · Multiple select

The compound(s) which show(s) the perovskite structure in solid state is (are)

$\mathrm{CaTiO_3}$
$\mathrm{NiFe_2O_4}$
$\mathrm{Fe_3O_4}$
$\mathrm{CsPbI_3}$

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Correct answer: (A) $\mathrm{CaTiO_3}$; (D) $\mathrm{CsPbI_3}$

Explanation

The **perovskite** structure has the formula $ABX_3$, where A is a large cation (12-coordinate), B is a smaller cation (6-coordinate) and X is an anion (oxide or halide).

**$\text{CaTiO}_3$:** the mineral perovskite itself ($\text{Ca}^{2+}$, $\text{Ti}^{4+}$, $\text{O}^{2-}$). ✓
**$\text{NiFe}_2\text{O}_4$:** an inverse **spinel**, $AB_2O_4$. ✗
**$\text{Fe}_3\text{O}_4$:** magnetite, also an (inverse) **spinel**. ✗
**$\text{CsPbI}_3$:** a halide perovskite ($\text{Cs}^+$ as A, $\text{Pb}^{2+}$ as B, $\text{I}^-$ as X), used in solar cells. ✓

Answer **A and D**.