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Perovskites: crystal structure, important compounds and properties

Perovskites: crystal structure, important compounds and properties. A 2+. B 4+. O 2-. Very stable structure, large number of compounds, variety of properties, many practical applications. Key role of the BO 6 octahedra in ferromagnetism and ferroelectricity.

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Perovskites: crystal structure, important compounds and properties

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  1. Perovskites: crystal structure, important compounds and properties

  2. A2+ B4+ O2- Very stable structure, large number of compounds, variety of properties, many practical applications. Key role of the BO6 octahedra in ferromagnetism and ferroelectricity. Extensive formation of solid solutions  material optimization by composition control and phase transition engineering. Ideal cubic perovskite structure (ABO3)

  3. Oxygen Octaedra Octaedral site B cations : Nb, Ta, Ti,Zr, Fe, Mn, …. Dodecaedral site A cations : K, Na, Ca, Sr, Ba, Pb, Bi, Y, La, … Cubic perovskite SrTiO3

  4. A2+ B4+ O2- Distorted perovskite structure (CaTiO3) Goldschmidt’s tolerance factor The perovskite structure is stable when 0.89  t 1.06 (taking rO = 0.14 nm). Ideal cubic structure only observed at room temperature when t is close to 1. If A ions are small, t <1, and tetragonal, orthorhombic and rhombohedral deformations of structure due to rotation and tilting of the BO6 octahedra are observed. Other types of deformations are induced by the appearance of spontaneous polarization in ferroelectric perovskites. Because of its flexibility, the perovskite structure can accommodate ions with different size and charge (AIBVO3, AIIBIVO3, AIIIBIIIO3) and the same site can be shared by ions with different charge (Ba(Mg1/3Nb2/3)O3 , Pb(Mn1/3Nb2/3)O3). The perovskite structure provides the building blocks for the assembly of other important crystal structures: Roddlesden-Popper phases (Can+1TinO3n+1), Aurivillius compounds ((Bi2O2)2+(Bim-1TimO3m+1)2-) and oxygen-deficient brownmillerite compounds (CaAlFeO5) Ideal cubic perovskite structure (SrTiO3)

  5. BO6 A Orthorhombic perovskite ABO3

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