Physics – Condensed Matter – Materials Science
Scientific paper
2007-06-15
Phys. Rev. B 76, 134101 (2007)
Physics
Condensed Matter
Materials Science
Replaced with extended version
Scientific paper
10.1103/PhysRevB.76.134101
We present a detailed study of the structural behavior and polarization reversal mechanism in phase III of KNO$_3$, an unusual ferroelectric material in which the nitrate groups rotate during polarization reversal. This material was one of several studied in a previous work [O. Di\'eguez and D. Vanderbilt, Phys. Rev. Lett. {\bf 96}, 056401 (2006)] where methods were described for computing curves of energy versus electric polarization. In the present work we extend and systematize the previous first-principles calculations on KNO$_3$, and analyze in detail a two-parameter model in which the energy of the system is written as a low-order expansion in the polarization and the nitrate group orientation. We confirm that this model reproduces the first-principles results for KNO$_3$ very well and construct its parameter-space phase diagram, describing regions where unusual triple-well potentials appear. We also present first-principles calculations of KNO$_3$ under pressure, finding that its energy-versus-polarization curves change character by developing a first-derivative discontinuity at zero polarization.
Diéguez Oswaldo
Vanderbilt David
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