Covalency driven modulation of paramagnetism and development of lone pair ferroelectricity in multiferroic Pb3TeMn3P2O14

Abstract

We have investigated the structural, magnetic and dielectric properties of Pb-based langasite compound Pb 3 TeMn 3 P 2 O 14 both experimentally and theoretically in the light of metal-oxygen covalency, and the consequent generation of multiferroicity. It is known that large covalency between Pb 6p and O 2p plays instrumental role behind stereochemical lone pair activity of Pb. The same happens here but a subtle structural phase transition above room temperature changes the degree of such lone pair activity and the system becomes ferroelectric below 310 K. Interestingly, this structural change also modulates the charge densities on different constituent atoms and consequently the overall magnetic response of the system while maintaining global paramagnetism behavior of the compound intact. This single origin of modulation in polarity and paramagnetism inherently connects both the functionalities and the system exhibits mutiferroicity at room temperature.

Short-range magnetic correlation and magnetodielectric coupling in multiferroic Pb3TeMn3P2O14

“…There are few compounds such as Ca 3 Co 2 O 6 , Er 2 BaNiO 5 , etc., which show displacive-type ferroelectricity involving offcentering of the magnetic ion due to short-range magnetic correlation 27,28 . Another one langasite compound Pb 3 TeMn 3 P 2 O 14 (our earlier work) which shows cova-lency driven modulation of paramagnetism and development of ferroelectricity 29 . In this case, a clear ferroelectric transition is developed near 310 K. Stronger Mn-O covalency redistributes the charges among the other cation-oxygen bonds, which in turn induces crucial electronic changes and consequently, the individual elemental magnetic moment gets changed in the system.…”

Short range magnetic correlation, metamagnetism and coincident dielectric anomaly in Na$_5$Co$_{15.5}$Te$_6$O$_{36}$

“…Due to rather tiny changes in position coordinates across the phase transition, the present Rietveld refinements could not conclusively determine the true symmetry of low temperature phase. Such difficulties are not unusual when the lattice distortions are weak 6,22 . However, it is interesting to note that the observed anomalies in a, b, c, and volume at around 155 K coincide with the magnetic and dielectric anomalies, as can be observed in Fig.…”

“…There are several mechanisms for developing ferroelectricity in this class of multiferroioc materials, such as i) ferroelectricity due to lone pair (PbTiO 3 , Pb 3 TeMn 3 P 2 O 14 , BiMnO 3 , BiFeO 3 , SnTiO 3 etc.) [5][6][7][8][9][10] , ii) ferroelectricity due to charge ordering (Pr 0.5 Ca 0.5 MnO 3 , RMnO 3 , TbMn 2 O 5 , LuFe 2 O 4 ) [11][12][13][14] , iii) geometric ferroelectricity (YMnO 3 ) 15 etc. But in case of improper multiferroicity, ferroelectricty appears due to the devel- * mssr@iacs.res.in opment of particular spin order which breaks the lattice inversion symmetry through exchange striction, thereby inducing a small amount of spontaneous polarization (∼10 −2 µC/cm 2 ) 3,4 .…”

“…Another langasite compound Pb 3 TeMn 3 P 2 O 14 which shows covalency driven modulation of paramagnetism and development of ferroelectricity 6 . Co based compounds are important in this con-text, where possible existence of different Co-oxidation states (+2, +3 and +4), with several local coordinations (tetrahedra, octahedra, trigonal prism and so on) around Co and most importantly various spin states within same Co valance often offer intriguing physical properties [23][24][25] .…”

Chemical design of a new displacive-type ferroelectric

“…15f, the net polarization arising from Pb 2+ hexagons and distorted TeO 6 octahedra is shown by arrows (purple for Pb 6 and red for TeO 6 ). As a derivative of Pb 3 TeCo 3 P 2 O 14 , Pb 3 TeMn 3 P 2 O 14 127 is known to show ferroelectricity via a mechanism similar to that in Pb 3 TeCo 3 P 2 O 14 . In the case of Pb 3 TeMn 3 P 2 O 14 , the T c is 310 K.…”