Low-temperature ground state structure of PbTiO3
2Department of Functional Materials, Institute for Problems of Materials Science Nas Ukraine, Kyiv, Ukraine
3Faculty of Mathematics and Physics, Charles University in Prague, Prague, Czech Republic
4Department of Dielectrics, Institute of Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic
5Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, USA
Lead titanate (PbTiO3) is one of the well-studied ferroelectric materials [1]. It has a simple cubic perovskite structure at T > 763 K which transforms into the tetragonal P4mm polar structure below this temperature. The ferroelectric phase transition is of the first order with the ratio of lattice constants c/a = 1.06 at 296 K. Besides the importance of the applications of this material, its physical properties are still attracting much attention from scientists. One of the most interesting problems in PbTiO3, that has not yet been completely solved, is whether this ferroelectric material undergoes other transition (or transitions) at low temperatures like many other ferroelectric perovskites, e.g. BaTiO3, KNbO3, NaNbO3.
In this report, we present our results of the detailed Mn4+, Cr3+ and Fe3+ electron paramagnetic resonance (EPR), 47,49Ti and 207Pb nuclear magnetic resonance (NMR) measurements carried out in PbTiO3 single crystals at temperatures from 300 K down to 20 K. It was found that the tetragonal crystal field parameter of the Mn4+ and Cr3+ impurity ions undergoes an unexpected change in its temperature dependence at T < 170 K: it increases with decreasing temperature to 150-170 K and then strongly decreases with further temperature lowering. Electric field gradient (EFG) at Ti site measured from 47,49Ti NMR shows non-uniform change with decreasing temperature: it sharply increases with decreasing temperature to 150-170 K and is practically temperature independent below these temperatures. Moreover, substantial broadening of NMR linewidth is seen for Ti and Pb nuclei at T < 170 K due to essential increase of lattice parameters fluctuations. All these facts may indicate proximity of a transition to another phase with barely perceptible crystal structure modification like reported by J. Kobayashi, Y. Ueda, Y. Sakemi, Phys. Rev. B 28, 3866 (1983) while, actually, it was not detected in NMR.
The support of the GA CR under projects No. 23-05578S and 19-28594X are gratefully acknowledged.
[1] M. E. Lines, A. M. Glass, Principles and application of ferroelectrics and related materials (Clarendon Press, Oxford, 1977).
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