The compositional dependence of octahedral tilting in orthorhombic and tetragonal perovskites

Abstract

A new parameterization is defined for the quantitative description of octahedral tilting in orthorhombic and tetragonal perovskites. It contains six parameters, s 1, s 2, s 3, 0 x, Oy and 0 z. s I , s 2 and s 3 refer to the lengths of the lines or 'stalks' joining pairs of opposite octahedral vertices, and 0 x, 0y and 0 z to the angles subtended by these stalks with pseudo-cubic axes x, y and z. An equation is derived for the dependence of polyhedral volume ratio, V a / V B, on these parameters: Va/V s = 6cos 2 0,. cos0z -1, where 0,, = (0, + Oy)/2. To a good approximation, lengths s~, s 2 and s 3 do not affect Va/V B. The validity of this equation is tested by reference to the known crystal structures of 48 temary oxide and fluoride perovskites, and its versatility demonstrated by application to the structures of some ternary palladium and platinum hydrides. The relationship of the approach to Glazer's system of nomenclature for octahedral tilting in perovskites is considered, in particular concerning the numbers of tilts operative in a given structure. A comparison is also made with the parameterization proposed for octahedral tilting and distortion in rhombohedral perovskites [Thomas & Beitollahi (1994). Acta Cryst. B50, 549-560]. Factors governing the choice of rhombohedrai or orthorhombic symmetry are discussed, with the significance of rhombohedral symmetry in obtaining ferroelectric properties brought out. Through the compilation of a table of AOl2 and BO 6 polyhedral volumes, the prospect is identified of predicting both the degree of octahedral tilting and the likelihood of ferroelectric behaviour for novel, hypothetical oxide compositions.

Interplay between antiferrodistortive, ferroelectric, and superconducting instabilities inSr1−xCaxTiO3−Lima1, Luz2, Oliveira3 et al. 2015Phys. Rev. B323430View full textAdd to dashboardCite

“…The distortion specific to SrTiO 3 , the clockwisecounterclockwise rotation of adjacent octahedra in a single (001) plane (dubbed antiferrodistortive), is one of the possible twenty-three octahedra tilts in the ABO 3 sys- tem, which were first classified by Glazer [36] and subsequently discussed by other authors [37,38].…”

Local structure of NaNbO3: A neutron scattering study

“…In particular Saito, et al 4 have designed a new lead-free ferroelectrics based on the MPB in the perovskite-rich region of (K,Na)NbO 3 , which shows excellent piezoelectric performance comparable to those of PZT. Interestingly their mother compound, sodium niobate, NaNbO 3 , is known for its complex phase behavior, and there are a number of conflicting reports on its structure [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] . Thus there is a strong need for understanding the structure and phase transformation of sodium niobate.…”

Structural Phase Transition of Orthorhombic LaCrO3 Studied by Neutron Powder Diffraction

“…7. < /< of various known samples (15,16, 25}29) having orthorhombic (space group Pnma) and rhombohedral (space group R3 c) structure are also included in the "gure. The rhombohedral samples tend to have smaller tilts and larger < /< values.…”