Why Pb(B1/3B'(2/3)) O3 Perovskites Disorder More Easily than Ba(B1/3B'(2/3)) O3 Perovskites and the Thermodynamics of (1:1)-Type Short-Range Order in PMN

Published

February 1, 2000

Author(s)

Benjamin P. Burton

Abstract

Fully relaxed, planewave pseudopotential calculations of formation energies (δE) were performed for ordered supercells in the perovskite based system (1 - X) PbNbO₃ - (X).PbMgO₃, including six different supercells at the X = 1/3 composition [Pb(Mg _1/3Nb_2/3)_O3; PMN. Some of the corresponding supercell calculations were also performed for the systems Pb(Zn _1/3Nb_2/3)O₃ (PZN), Pb(Mg_1/3Ta_2/3)O₃ (PMT) and Ba(Zn_1/3Ta_2/3)O₃ (BZT). A striking difference between the PMN results and those for PZN, PMT and BZT is that all the PMN formation energies are within - 4 kJ/(ABO₃ - mole), which indicates a very low energy barrier to disordering. The BZT results by contrast, span a range of at least - 40 kJ/mole, consistent with a very stable ordered ground state (GS) phase. The (δE) results suggest a candidate GS for PMN in which (Nb)-layers alternate with chessboard layers perpendicular to [001] cubic. Ising type thermodynamic models, that are roughly consistent with the )+ results, were used to simulate the finite temperature behavior of a prototype A(B_1/3B'_2/3)O₃ perovskite that exhibits the transition sequence (1 : 2) -> (1 : 1)-> Disordered. This model reproduces the characteristic microstructure of PMN, and explains it in terms of equilibrium (1 : 1) short range order in the disordered phase.

Citation

Journal of Physics and Chemistry of Solids

Volume

61

Issue

No. 2

Pub Type

Journals

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Keywords

first principles, order-disorder, phase disgram, PMN

Citation

Burton, B. (2000), Why Pb(B_1/3B'_(2/3)) O₃ Perovskites Disorder More Easily than Ba(B_1/3B'_(2/3)) O₃ Perovskites and the Thermodynamics of (1:1)-Type Short-Range Order in PMN, Journal of Physics and Chemistry of Solids, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=850280 (Accessed April 30, 2024)