摘要:

Current solid state actuators are briefly compared to traditional actuator technologies to highlight the major need for enhanced strain capability. For the ferroelectric piezoelectric polycrystal ceramics, the balance of evidence suggests a large entrinsic contribution to the field induced strain from ferroelectric-ferroelastic domain wall motion. Here-to-fore the intrinsic single domain contribution has been derived indirectly from phenomenological analysis. Now, new evidence of a stable monoclinic phase at compositions very close to the MPB suggest that the previous assessment will need to be revised. Actuator behavior in the new lead zinc niobate-lead titanate (PZN:PT) single crystal shows most unusual anisotropic behavior. For 111 oriented field poled crystals in the rhombohedral phase normal low induced strain is observed. For 001 field poled crystals however massive (0.6&percent;) quasi-linear anhysteritic strain can be induced. Since the 001 oriented field in the rhombohedral phase can not drive ferroelastic domain walls it is suggested that the strain must be intrinsic. The suggestion is that it is due to an induced monoclinic phase in which the Ps vector tilts under increasing field up to more than 20° from 111, before the vector switches to the tetragonal 001 direction. Such a polarization rotation mechanism has also been suggested by Fu and Cohen. Calculations of induced single domain strain using measured electrostriction constants agree well with observed behavior. Recent measurements by Park &etal; and Wada &etal; on single crystalBaTiO3show strongly enhanced piezoelectricity at temperatures near the ferroelectric phase transitions. Of particular relevance is the inverse experiment forcing the tetragonal over to the rhombohedral phase with high 111 oriented field. From this result it is suggested that both cubic and dodecahedral mirrors participate in the reorientation through orthorhombic to the rhombohedral state giving rise to different value of the inducedd33at different field levels. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324434

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

In spite of the success of electron theories to account for the ferroelectric phenomena, ideas in classical crystal chemistry are still useful in unraveling complex behavior of multicomponent solids. In particular they provide a natural explanation of high susceptibilities of mixed-ion systems based upon the concept of competing interactions. However, they are largely phenomenological and empirical. It is suggested that the concept of atomic level stresses can bridge the gap between the crystal chemistry approach and first-principle calculations in a most meaningful way. Also some novel experimental methods, which directly probe certain aspects of the electronic state relevant for this phenomenon, are discussed. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324435

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Relaxor properties ofSr0.61−xBa0.39Nb2O6:Cex3(SBN61:Ce) are examined by dielectric spectroscopy and linear birefringence (LB) as a function of frequency and temperature before and after poling. Relaxor behavior with large polydispersivity is observed above the ferroelectric phase transition temperatureTc.BelowTca long-range ordered ferroelectric state with low polydispersivity prevails. An Ornstein-Zenike analysis ofLBdata suggests that pureSBN61belongs to the3DIsing universality class. Doping withCe3−ions, which seem to act as random fields, enhances the relaxor properties and drives the system towards the random-field Ising model (RFIM) universality class. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324436

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

To check whether the recently proposed SRBRF model also adequately describes the relaxor to ferroelectric transition the temperature dependence of the static dielectric constant of PMN has been fitted to the SRBRF model. The results show that in contrast to dipolar glasses the mean coupling constantJ0is here indeed close to the root mean square varianceJ. ForE⩾EC J0can therefore become bigger thanJresulting in a transition from a relaxor to a ferroelectric state. The relaxor to ferroelectric cross-over in the non-linear dielectric responsea3=&khgr;3/&khgr;l4in the form predicted by the SRBRF model forE⩾EChas been observed in PLZT ceramics. The temperature dependence of the Edward-Anderson order parameterqhas been determined via NMR in PSN in the region of the ferroelectric transition and as well shows theT-dependence predicted forJ0>J.The relaxor to ferroelectric transition can be thus well described by the SRBRF model. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324437

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Extended thermal annealing treatments were used to modify the B-site cation order in the(1−x)PMN−(x)PSNperovskite system. Extensive 1:1 ordering could be induced in compositions withx⩾0.1.The substitution of PSN into PMN produces a large increase in the thermal stability of the 1:1 ordered phase, with the maximum disordering temperature of ∼1360&hthinsp;°C being observed forx=0.5.The order-disorder transition temperature for pure PMN was calculated to be 913&hthinsp;°C. The changes in stability could be rationalized using the random site model for the cation order. The well ordered, large chemical domain ceramics exhibited relaxor behavior up tox∼0.6,for higher values normal ferroelectric behavior was observed. Alterations in the size of the chemical domain size had no significant effect on the properties of the lower x compositions, but induced a transition to relaxor behavior forx>∼0.6.©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324438

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Lead Magnesium Niobate (PMN) displays a superstructure characterized by the presence of broad half-order diffraction peaks. The structure is known to involve chemical ordering between alternate B sites within small domains. It has been proposed that this might be due to small domains of Mg:Nb chemical ordering with full 1:1 stoichiometry. Such order is inconsistent with the bulk composition ofPbMg1/3Nb2/3O3and would lead, moreover, to a net charge of−12eper unit cell. In this work we report our resonant X-ray diffraction experiments designed to distinguish 1:1 from bulk-stoichiometric ordering. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324439

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We present a phenomenological model of ferroelectricity that quantitatively accounts for both displacive like and order-disorder like properties of pure perovskite ferroelectrics. We further show that this model also accounts for the dielectric and phase transition properties of incipient ferroelectrics doped with off-center impurities. Finally, we present a microscopic model that quantitatively shows that the off-center displacements in a number of perovskites is a manifestation ground state polarons. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324440

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The insulating state of matter is characterized by the excitation spectrum, but also by qualitative features of the electronic ground state. The insulating ground wavefunction in fact: (i) displays vanishing dc conductivity; (ii) sustains macroscopic polarization; and (iii) islocalized. The idea that the insulating state of matter is a consequence of electron localization was first proposed in 1964 by W. Kohn. I discuss here a novel definition of electron localization, rather different from Kohn’s, and deeply rooted in the modern theory of polarization. In fact the present approach links the two features (ii) and (iii) above, by means of essentially the same formalism. In the special case of an uncorrelated crystalline solid, the localization of the many body insulating wavefunction is measured according to our definition by the spread of the Wannier orbitals; this spread diverges in the metallic limit. In the correlated case, the novel approach to localization is demonstrated by means of a two-band Hubbard model in one dimension, undergoing a transition from band insulator to Mott insulator. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324441

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The first-principle-derived approach proposed in Ref. [1] is used to study structural properties ofPb(Zr0.5Ti0.5)O3alloys at finite-temperature. Predictions are in excellent agreement with experimental data and direct first-principles results. Other possibilities offered by this approach are also discussed. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324442

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We have performed a first-principles study of the zone-center optical modes of hexagonalBaTiO3,showing that all the experimentally relevant low-energy modes are characterized by the same local polar distortions that determine the ferroelectric instability of the cubic perovskite. The influence of the particular stacking of theTiO6groups in the hexagonal structure and the occurrence of previously unreported low-energy Rigid Unit Modes are addressed. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1324443

出版商:AIP    

年代:1900

数据来源: AIP