The Basic Properties Of Tb₂（MoO₄）₃ And Its Multiferroic Research

Multiferroics means at least two primary ferroic properties, namely of ferroelectricity, ferromagnetism or ferroelasticity in one single homogeneous phase, which also includes anti-ferroelectricity, anti-ferromagnetism. The coupling between these ferroic orderings makes the mutual control of different ferroic properties become possible, for which multiferroic materials are of new multi-functional and have broad application prospects in spintronics, multi-phase memories, sensors and other technical areas. In condensed matter physics, multiferroics itself has raised a number of fundamental issues and challenges in electrics, magnetism and strongly correlated electron physics and become an intensive interest of research in quantum controlling. In recent years, the revival of multiferroics has made great progress.Recently, multiferroic research has been focused on ferroelectric, (anti-) ferromagnetic coupling in single-phase and composite materials. The multiferroic research upsurge recent years induces a comprehensive understanding to multiferroic physics and successfully explores the potential applications. The observation of multiferroic properties in ReMnO3 and BiFeO3 initiated intensive study on single phase multiferroic materials and put forwarded some new micro-mechanisms, but there are still some problems in these new mechanisms. Up to now, most single phase multiferroic materials have very weak magnetic properties even exhibit ferromagnetism only at low temperatures, which is a serious obstacle in application. These years, the major breakthrough in magnetoelectric (ME) effect is obtained in the ME composite materials, such as piezoelectric/magnetostrictive laminate materials as well as self-organized nano-scale columnar compound and so on, in which the ME coupling is achieved through the stress transmission. At present, some of the piezoelectric/ferromagnetic composites are of great possibility to be used in applications. Due to the increasing demand of miniaturization and flexibility in application, artificial superlattice becomes a new interest in Condensed Matter Physics and Materials Science. Artificial materials exclude some natural limitations and show new physical phenomena. Such as, Duan et al. proposed on the basis of first principles calculation that the Fe/BaTiO3 (BTO) supper lattice structure could realize magnetism controlling by electric field; tricolor materials LaAlO3/La0.6Sr0.4MnO3/SrTiO3 may get electric polarization at the interface. These physical mechanisms are still not clear and need further investigation.In this article, we mainly focus on the ferroelectric-ferroelastic Tb2(MoO4)3 crystal. First, we studied the basic physics properties of Tb2(MoO4)3 crystal systemically. Second, the 2-2 type Terfenol-D/Tb2(MoO4)3 laminate composites were synthesized which combined three ferroic order (ferroelectric, ferroelastic and ferromagnetic). We confirmed a strong influence of shear strain on the ME effect. Because of the lack of the attention on ferroelasticity in multiferroic research, we emphasized the ferroelastic influence on the laminate composite. Third, the luminescence of lanthanon had drawn significant interest for a long time, especially Eu and Tb. We studied the luminescence property of Tb2(MoO4)3 crystal and explained the luminescence mechanism. Associated with the other optical properties, we provided the future analysis and comparison. At last, we synthesized the Tb2(MoO4)3 ceramics and studied its properties. The innovative achievements are as follows:1. The research on the basic properties of Tb2(MoO4)3 crystal, including thermodynamics, ferroelectric property, dielectric property, optical property, ferroelastic effect and Raman spectrum was taken. The Tc of Tb2(MoO4)3 was confirmed and the phase change was first order. The ferroelectric property of Tb2(Mo04)3 crystal was measured. Meanwhile, we found the dielectric tunability in Tb2(Mo04)3 crystal which may be caused by ferroelectric property, electrical defects or electron hopping of Tb iron. Besides the dielectric peak at Tc, studies on the temperature dependence of dielectric constant (e) and loss factor (tan δ) measured at various frequencies showed the existence of dielectric relaxation which may originated from the dipolar effects associated with the charge carrier hopping between Tb3+and Tb4+. The optical properties had been studied including transmission spectrum and refractive index. We fitted the ferroelastic loop through the strain-stress loop which had been measured. The Raman spectrum of the Tb2(MoO4)3 was observed and the vibration modes corresponding to the phonon peaks were analyzed.2. The magnetoelectric effect of 2-2 Terfenol-D/Tb2(MoO4)3 laminate composite had been studied. Through calculation from the piezoelectric matrix, we found the shear strain could provide the contribution to magnetoelectric effect besides the normal strain. The maximum of magnetoelectric coupling coefficient was 12V/(cm Oe) at the resonance frequency. Also hypo-resonance frequencies were observed at lower frequencies which may be attributed to the bending libration resonance. The magnetoelectric coupling coefficient had a linear relationship with invigorative ac magnetic field which could be applied in the detection of ac small magnetic field. At last we inferred the influence of ferroelastic phase on magnetoelectric composite including ferroelectric, ferroelastic, ferromagnetic phase and the nonzero magnetoelectric output and magnetoelectric loop as butterfly measured confirmed the ferroelastic effect.3. The luminescence of Tb2(MoO4)3 had been studied. The photoluminescence peaks at 490 nm,540 nm,580 nm,615 nm respectively are now observed, indicating additional energy bands with maxima at 2.54,2.28,2.12, and 1.99 eV. These bands are attributed to the 5D4â†'7F6,5D4â†'7F5,5D4â†'7F4 and 5D4â†'7F3 transitions of Tb3+ ions, respectively. The energy of excitated wavelength of 486 nm is 2.55 eV which is equal to the transition energy from 5D4 to 7F6, so the electron transition of 5D4â†'7F6 is the reason for the absorption of light of 486 nm and the strong luminescence excitated by the light of 486nm. Additionally, the photoluminescence spectrum of Tb2(MoO4)3 powder dispersed equably in the water solution is measured. The peak of photoluminescence at 490 nm,540 nm,580 nm,615 nm can also be found except the peak around 400 nm which is caused by the Raman scattering of the water and the peak of 464 nm which comes from the xenon lamp as the excitation. Compared with the luminescence intensity of (Tb0.99Co0.01)2(MoO4)3 and (Tb0.99Cr0.01)2(MoO4)3, we found the luminescence intensity of Co3+ doped crystal decreased, but the one of Ce3+ doped crystal increased. The origin needed future research.4. The Tb2(MoO4)3 ceramics had been synthesized and its basic properties were measured including ferroelectric property, dielectric relaxor, magnetic property and phase change. The dielectric relaxation was observed in the Tb2(MoO4)3/CoFe2O4 composite which may come from the charge carrier or oxygen vacancies. The ferroelectric, ferromagnetic and magnetoelectric property had been studied in Tb2(MoO4)3/CoFe2O4 0-3 composite.