Gil de Cos, Gerardo
[Author];
Torres, M.E
[Author];
González-Silgo, C.
[Author];
Soler-Carracedo, Kevin
[Author];
Martín, Inocencio R.
[Author];
Rivera-López, F.
[Author];
Rodríguez-Rodríguez, S.
[Author]
Unexpected Wide Tuning of Ferroelectric Properties by Varying the Er Concentration in La2-Xerx(Moo4)3 (X = 0.75, 1, 1.25) Solid Solutions
Description:
Powder samples of the series of trimolybdates rare earths (RE) with formula La 2-x Er x (MoO 4 ) 3 (for x = 0.75, 1, 1.25) were prepared by solid-state reaction from the end compounds La 2 (MoO 4 ) 3 and Er 2 (MoO 4 ) 3 . The correlation of the ferroelectric properties with the crystal structure, as a function of the x concentration, was analyzed by X-ray diffraction (XRD), dielectric spectroscopy, the ferroelectric hysteresis loop, and optical emission spectroscopy. X-ray diffraction patterns were refined by a non-conventional Rietveld method following the ferroelectric structure of the β'-Gd 2 (MoO 4 ) 3 type. One primary and two secondary modes were distinguished, like in similar improper ferroelectrics, from a symmetry mode analysis of the paraelectric-ferroelectric phase transition. The two non-equivalent coordination environments of RE atoms in the crystal structure differed slightly by lengthening or shortening the atomic bonds, depending on the higher or lower lanthanide occupation. From the ferroelectric hysteresis loop, maximum and remanent polarization increased with the Er concentration and according to the amplitude of the polar (secondary) symmetry mode. Moreover, dielectric and Er 3+ emission spectroscopy displayed the weak ferroelectric-paraelectric transition for x = 1 and x = 1.25 at different temperatures.Contrary to the expectations, the ferroelectric properties intensify as the Er 3+ concentration increased. For instance, the maximum polarization for La 0.75 Er 1.25 (MoO 4 ) 3 reaches one order of magnitude larger than for La 1.25 Er 0.75 (MoO 4 ) 3 , and the Curie temperature is better detected and increases around 200 K. This unexpected behavior is the opposite of the behavior observed for the family of improper ferroelectrics RE 2 (MoO 4 ) 3 , where the ferroelectric properties enhanced slightly when the RE ionic radius increased. Hence, the series La 2-x Er x (MoO 4 ) 3 allows an improved and wide tuning range of the ferroelectric properties. This feature adds interest in Er 3+ emission (e.g., down and upconversion) in these multiferroic crystalline matrices