摘要:

The influence of pressure on the dielectric properties and phase behavior was investigated for two substituted single crystals of SrTiO3: (a)18O exchanged SrTi18O3[STO‐18] and (b) lightly doped Sr1−xCaxTiO3with x = 0.007 [SCT (0.007)]. The18O atoms in STO‐18 reduce both the quantum fluctuations of the TiO6octahedra and the frequency of the soft phonon mode, leading to a ferroelectric (FE) state via a first‐order transition with Tc∼ 24 K at 1 bar. Tcdecreases very rapidly under pressure with an initial slope of ∼ 20 K/kbar, reaching the quantum displacive limit (Tc= 0 K) near 0.7 kbar. In the case of SCT (0.007), fluctuating polar nanodomains surround the off‐center Ca dopants and grow in size as the correlation length for dipolar interactions in the SrTiO3host increases with decreasing temperature. Ultimately, the fluctuations slow down and the nanodomains “freeze” into a relaxor state with Tmax∼ 18 K; pressure reduces Tmaxwith an initial slope of ∼ 35 K/kbar. Both the FE transition in STO‐18 and the relaxor state of SCT (0.007) are completely suppressed below 1 kbar and a quantum paraelectric state emerges. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1609931

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Two complex perovskite antiferroelectric (AFE) systems were studied; they are Pb0.97La0.02(Zr0.6Sn0.3Ti0.1)O3(PLZST) in ceramic form and Pb0.99Nb0.02(Zr0.82Sn0.12Ti0.04)0.98O3(PNZST) in thin film form. Dielectric and transmission electron microscopy (TEM) studies of the PLZST ceramics confirmed the AFE nature of the specimen, but at low temperature the electrical field application could induce a temporary ferroelectric (FE) phase with characteristic life‐time dependent on temperature This life‐time reaches a value of ∼ 0.1s at 248K. Further decrease of temperature leads to a much faster than Arrhenius growth of the recovery time, which eventually exceeds the reasonable laboratory time scale below 210K. We believe that the strongly temperature‐dependent kinetics arises from a cooperative freezing of the incommensurate AFE order in the presence of quenched composition disorder. The PNZST films’ polarization properties are highly dependent on the film thickness and at the lowest studied limit (∼170 nm) the field application in the surface normal direction can induce the FE phase with the time of recovery back to the AFE state being a magnitude of several hours. In this case the filed‐induced FE ordering is very asymmetric with respect to the field direction, is thickness dependent and the FE phase can be induced if the time of field application is on scale of a second. The application of the field for a much shorter time (e.g. 1ms) does not significantly affect the AFE properties of the film. We suggest that the substrate/film interface could be responsible for this phenomenon. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1609932

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

A quadrupole coupling induced47Ti and49Ti satellite background is observed in the cubic phases of BaTiO3, SrTiO3and oxygen 18 enriched SrTi18O3. The satellite background demonstrates that all Ti ions are dynamically disordered between several off‐center sites. No splitting or broadening of the central Ti 1/2 → −1/2 NMR transitions is seen on going through the “ferroelectric” transition in SrTi18O3atTc= 25 K. It seems that in contrast to BaTiO3the Ti disorder is still present. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1609933

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Two different non‐Debye dielectric spectra are observed in different low‐frequency regimes in a polydomain relaxor ferroelectric single crystal, SrTi18O3, below its transition temperature,Tc≈ 23 K. Atf< 1 kHz the response is due to irreversible creeplike wall motion, &khgr;′ ∝ &khgr;″ ∝ &ohgr;−&bgr;with &bgr; ≈ 0.1 while polydispersive reversible wall segment relaxation with pink noise character is encountered at higher frequencies,f> 1 kHz. The crossover between both kinds of dielectric response is attributed to a dynamical phase transition [Nattermann et al., 2001]. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1609934

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Aging and noise are used to elucidate the types of frozen order formed in the relaxor regime. In PMN, PMN with 10&percent; PT, and PLZT aging deep in the relaxor regime shows several features characteristic of spinglasses, including multiple independent susceptibility ‘holes’ formed at different aging temperatures. This effect requires complex cooperative glassy freezing of many local units. However, the field scale required to disrupt the aging is anomalously high compared to spinglasses, if a nanodomain is the unit corresponding to a spin. Barkhausen noise results imply cooperative moment changes involving several nanodomains near Tg, but much smaller steps below Tg. This result suggests that kinetic barriers increase at Tgwithout increasing coupling among nanodomains. Together, these results suggest that in prototypical relaxors the glassy state is not formed by nanodomains, although it affects their dynamics, but rather by smaller units. We tentatively propose that the canted components of the local polarizations (found in scattering experiments) are analogous to the x‐y spins in a reentrant spinglass. The first tested prediction of this new picture is that spinglass‐like aging effects would be absent in the uniaxial ‘relaxor’ SBN. Such effects do vanish well below Tgin SBN. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1609935

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

In this paper, we present a microscopic model for heterogeneous ferroelectric and an order parameter for relaxor phase. We write a Landau theory based on this model and its application to ferroelectric PbFe1/2Ta1/2O3(PFT) and antiferroelectric NaNbO3:Gd. We later discuss the coupling between soft mode and domain walls, soft mode and quasi‐local vibration and resulting susceptibility function. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1609936

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Temperature dependence of the local structure of relaxor and related ferroelectric oxide systems, such as PMN, PST and PZT, are discussed based upon the results of the pulsed neutron atomic pair‐density function (PDF) analysis. Optical data have shown various changes in the local structure taking place much above the relaxor freezing temperature. However, the origins of such changes have long been controversial. We show that the Burns temperature is the local Curie temperature at which the polar nano‐regions are formed, and the transition is of the order/disorder type for Pb polarization. Local Pb polarization persists up to temperatures several hundreds of degrees above the Burns temperature where the Raman scattering suggests disappearance of the local distortion in the oxygen environment. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1609937

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Temperature dependent studies of the 1/2(hk0) superlattice reflections (&agr; spots) by synchrotron x‐ray scattering measurements were performed in Pb(Mg1/3Nb2/3)O3(PMN) and [PbMg1/3Nb2/3O3]1−x‐ [PbTiO3]x(PMN‐xPT) with Ti dopingx⩽ 0.32 single crystals. Separation of the &agr; spots from the underlying diffuse scattering background allowed studying them as separate entities for the first time. Structure factor calculations have shown that &agr; spots constitute the presence of a new kind of anti‐ferrodistortive nanoregions (AFR) in the form of fluctuations produced by anti‐parallel short‐range correlated ⟨110⟩ Pb2+displacements. AFR appear to be different and unrelated to the chemical nanodomains (CND) and ferroelectric polar nanoregions (PNR). Simultaneous presence of AFR and PNR can explain relaxor behavior as a result of competition between randomly occurring ferroelectric and anti‐ferroelectric fluctuations. Temperature dependence of the &agr; spots in PMN showed a direct correlation with the freezing phase transition near Tf≈220 K. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1609938

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Micro‐Brillouin measurements on single crystal lead titanate were carried out at ambient conditions. We used a symmetrical scattering geometry that allows probing of all wave vectors within a given plane. All acoustic modes could be resolved. A central peak that is strongly coupled to the acoustic modes is observed. Detailed analysis of the coupling reveals the importance of the irreducible representation of symmetry E that is closely related to the ferroelectric phase transition at higher temperatures. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1609939

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Results of study of the spatial distribution of polarization by scattering (X‐ray and neutron) and Piezoresponse Force Microscopy techniques are presented for several relaxors both cubic (PMN and PMNPT solid solutions) and uniaxial (SBN). It is demonstrated that in all cases except pure PMN cooled in zero electric field polar nanodomains are formed. In case of PMN cooled in the applied field nanodomain state is preserved even after subsequent zero field heating to above freezing temperature. AFM measurements of PMNPT10 are used to determine the quantitative characteristics of these nanodomains. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1609940

出版商:AIP    

年代:1903

数据来源: AIP