New ferroelectric: Bis-thiourea pyridinium bromide inclusion compound
- PDF / 270,489 Bytes
- 7 Pages / 584.957 x 782.986 pts Page_size
- 4 Downloads / 143 Views
Eric Collet and Loic Toupet Université de Rennes 1, Institut de Physique de Rennes, UMR UR1-CNRS 6251, F-35000 Rennes, France
Jan Wa˛sickia) Faculty of Physics, Adam Mickiewicz University, 61-614 Poznan, Poland (Received 9 May 2012; accepted 21 August 2012)
Dielectric measurements (permittivity and hysteresis loop) of monocrystals of bis-thiourea pyridinium bromide inclusion compound have revealed for the first time ferroelectric properties of the studied samples. In the present article, a model of ferroelectric ordering on the basis of single-crystal x-ray diffraction data is described. In the low-temperature phase, the spontaneous polarization is directed along the a axis and ferroelectricity is of the mixed type (displacement and order-disorder component), whereas in the intermediate phase the spontaneous polarization is directed along the c axis and ferroelectricity is of the order-disorder type.
I. INTRODUCTION
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.301
type materials.22,24,25 However, the ferroelectric properties were not found in the halide pyridinium salts with spherical anions as with iodide, bromide, and chloride because of the antiparallel ordering of pyridinium cations. An interesting study was performed with pyridinium salts confined in the rigid entrapment made of thiourea molecules as a host sublattice. So far four such systems are known with the chloride, bromide, iodide, and nitrate anions, hereafter denoted as inclusion compounds of bis-thiourea pyridinium chloride (T2(PyH)Cl), bis-thiourea pyridinium bromide (T2(PyH)Br), bis-thiourea pyridinium iodide (T2(PyH)I), and bis-thiourea pyridinium nitrate (T2(PyH)NO3), respectively.26–28 In the first three systems the anion is spherical, whereas in the fourth—it is planar. These compounds have been intensively studied as to their structural,27,29 dynamic,3038 and possibly ferroelectric properties.27,29,39 Research of ferroelectric properties in the family of thiourea pyridinium salts inclusion compounds with pyridinium salts are important because, to the best of our knowledge, other thiourea inclusion complexes with organic molecules as guest are not ferroelectric materials. Recently, ferroelectric properties have been found in the low-temperature and intermediate phases of bis-thiourea pyridinium iodide inclusion compound [T2(PyH)I] and in the low-temperature phase of bis-thiourea pyridinium nitrate inclusion compound [T2(PyH)NO3].27 However, it should be emphasized that the hysteresis loop evidencing the ferroelectric character was recorded only for the low-temperature phase of bis-thiourea pyridinium iodide. A detailed analysis of the structural data has permitted to propose a model of ferroelectricity in these compounds. The ferroelectricity was found to be related with the ordering of the pyridinium cation and with the
2844
Ó Materials Research Society 2012
Intensive search for new ferroelectric materials is of continued interest for both pure theoretical research and practical application
Data Loading...
