Temperature-pressure phase diagram of ferroelectric Sn₂P₂S₆

P. Ondrejkovic¹, M. Kempa¹, M. Guennou¹, Y. Vysochanskii², P. Saint-Grégoire³, P. Bourges⁴, K. Z. Rushchanskii⁵, J. Hlinka¹

¹Institute of Physics of the Czech Academy of Sciences, Na Slovance 2, 18221 Praha 8, Czech Republic

²Institute for Solid State Physics and Chemistry, Uzhgorod University 88000, Uzhgorod, Ukraine

³Laboratory MIPA, Department of Sciences and Arts, University of Nimes, 30021 Nimes Cedex 1, France

⁴Laboratoire Leon Brillouin, Bat 563 CEA Saclay, 91191 Gif sur Yvette Cedex, France

⁵Peter Gruenberg Institut, Forschungszentrum Juelich GmbH, 52425 Juelich and JARA-FIT, Germany

ondrejkovic@fzu.cz

 

The temperature-pressure phase diagram of the ferroelectric semiconductor Sn₂P₂S₆ single crystal has been investigated by neutron and x-ray scattering techniques. The proposed phase diagram was rich in phases, and a special critical point where paraelectric, ferroelectric and incommensurate phases meet was predicted there [1]. We intended to prove the presence of the incommensurate phase by investigating temperature-pressure dependence of satellite and Bragg reflections as well as (quasi)elastic diffuse scattering. Therefore we have undertaken neutron and x-ray scattering experiments at LLB and ESRF, respectively [2,3]. We found that the H00 Brillouin zones are sensitive to the order parameter (polarization) and its fluctuations (see Figure 1). However we have observed only a direct paraelectric-ferroelectric phase transition without any incommensurate phase in the whole investigated pressure range (up to ~1.2 GPa) [3]. These results are in a clear disagreement with phase diagrams assumed in numerous earlier works, according to which a hypothetical intermediate incommensurate phase should be present in this region of the temperature-pressure phase diagram.

Figure 1. Temperature dependence of critical diffuse scattering and Bragg scattering near a phase transition in the temperature-pressure phase diagram of Sn₂P₂S₆ single crystal.

1. A.G. Slivka et al, Condens. Matter Phys. 2, 415 (1999).

2. P. Ondrejkovic et al, Phys. Rev. B 86, 224106 (2012);

3. P. Ondrejkovic et al, J. Phys.: Condens. Matter 25, 115901 (2013).