We show that the neutron diffuse scattering in relaxor ferroelectric
(1-x)PbZn$_{1/3}$Nb$_{2/3}$O$_{3}$ - x PbTiO$_{3}$ (x=0.07) consists of two
components. The first component is strictly elastic but extended in q-space and
grows below 600 K. The second component, that was not reported before for the
(1-x)PbZn$_{1/3}$Nb$_{2/3}$O$_{3}$ - x PbTiO$_{3}$ (x=0.07) relaxor
ferroelectrics, is quasi-elastic with a line-width that has a similar
temperature dependence as the width of the central peak observed by Brillouin
spectroscopy. The temperature dependence of the susceptibility of the
quasi-elastic scattering has a maximum at the ferroelectric transition

Gvasaliya S. N.

Günter P.

Kojima S.

Lushnikov S. G.

Roessli B.

Rotaru G.-M.

小島 誠治

Applied Physics Letters

English

arXiv

G.-M. Rotaru

S. N. Gvasaliya

B. Roessli

S. Kojima

S. G. Lushnikov

P. Günter

Crossref

Evolution of the neutron quasielastic scattering through the ferroelectric phase transition in 93%PbZn1∕3Nb2∕3O3–7%PbTiO3

KOJIMA Seiji

Tsukuba Repository  (Tulips-R)

Evolution of the neutron quasielasticscattering through the ferroelectric phasetransition in 93%PbZn1/3Nb2/3O3 7%PbTiO3著者 Rotaru G.-M., Gvasaliya S. N., Roessli B.,Kojima S., Lushnikov S. G., Gunter P.journal orpublication titleApplied physics lettersvolume 93number 3page range 032903year 2008-07権利 (C)2008 American Institute of PhysicsURL http://hdl.handle.net/2241/104084doi: 10.1063/1.2963474Evolution of the neutron quasielastic scattering through the ferroelectricphase transition in 93%PbZn1/3Nb2/3O3–7%PbTiO3G.-M. Rotaru,1,a S. N. Gvasaliya,1 B. Roessli,1 S. Kojima,2 S. G. Lushnikov,3 andP. Günter41Laboratory for Neutron Scattering, ETH Zurich and Paul Scherrer Institut, CH-5232 Villigen PSI,Switzerland2Institute of Materials Science, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan3Ioffe Physical Technical Institute, 26 Politekhnicheskaya, 194021 St. Petersburg, Russia4Institute for Quantum Electronics, ETH Hönggerberg-HPF, CH-8093 Zurich, SwitzerlandReceived 11 May 2008; accepted 1 July 2008; published online 23 July 2008We show that the neutron diffuse scattering in relaxor ferroelectric 1−xPZN−xPT x=0.07consists of two components. The first component is strictly elastic but extended in q-space andgrows below 600 K. The second component, which was not reported before for the 1−xPZN−xPT relaxor ferroelectrics, is quasielastic with a linewidth that has a similar temperaturedependence as the width of the central peak observed by Brillouin spectroscopy. The temperaturedependence of the susceptibility of the quasielastic scattering has a maximum at the ferroelectrictransition. © 2008 American Institute of Physics. DOI: 10.1063/1.2963474Complex perovskites with the chemical formulaPbB1/3Nb2/3O3 B=Mg, Zn are important materials for ap-plications because they possess giant piezoelectric constantswhen doped with PbTiO3 PT. The temperature-concentration phase diagrams of PbMg1/3Nb2/3O3 PMNand PbZn1/3Nb2/3O3 PZN are complex. The average crystalstructure of pure PMN is cubic at all temperatures. For smallconcentrations of PT there is a phase transition from cubic torhombohedral symmetry at low temperature. Upon increas-ing the amount of PT a morphotropic phase boundary thatseparates the rhombohedral phase from a phase withtetragonal symmetry appears at x=0.32 Ref. 1 for1−xPMN−xPT and x=0.08 Ref. 2 for 1−xPZN−xPT.The dielectric permittivity of PMN and PZN has a broadmaximum around 265 and 320 K, respectively. At highertemperatures the dependence of the refractive index of bothmaterials deviates from the expected linear dependence andthis was explained by the appearance in the crystals of polarregions of nanometer size PNR.3 Evidence for the forma-tion of PNR in 1−xPMN−xPT and 1−xPZN−xPTcomes from the presence of temperature-dependent diffusescattering DS close to the Bragg reflections observed byboth x rays and neutron diffraction. Upon approaching Tc,the intensity of the diffuse scattering increases which sug-gests that the PNRs grow and that the ferroelectric state inthe relaxor ferroelectrics is eventually reached when thePNRs produce a spontaneous polarization in the same direc-tion. Therefore it is of importance to understand the structureand dynamics of the PNRs. The local structure of the PNRshas still not be completely determined and whether or not thelocal symmetry of the PNRs is lower than cubic already athigh temperature or undergoes a local phase transition aboveor at Tc is a matter of debate.5,4 The diffuse scattering mea-sured by neutron scattering in 1−xPMN−xPT is not en-tirely static but has an additional quasielastic QE compo-nent that corresponds to the dynamics of the PNRs.6,7 ForPMN the intensity associated with the QE scattering wasfound to follow the temperature dependence of the dielectricpermittivity.8 The central peak CP and the QE componentare also observed in doped PMN by neutron scattering,9 al-though the CP intensity is weaker than in pure PMN. In1−xPMN−xPT with x=0.32 the susceptibility of the QEscattering increases below the Burns temperature and has abroad maximum at the temperature where the cubic-to-tetragonal phase transition occurs.91−xPMN−xPT and 1−xPZN−xPT solid solutionshave comparable x ,T-phase diagrams and the dielectric re-sponse of both undoped materials shows relaxor properties.In PMN and in PZN, it was shown by neutron scattering thatthe shape and the temperature dependence of the DS aresimilar, and it was proposed in Refs. 8–10 that a random-field model with cubic anisotropy could describe the physicalproperties of both families of compounds. In the attempt topropose a unified description of 1−xPMN−xPT and 1−xPZN−xPT relaxors, an unsolved question is the behaviorof the QE part of the diffuse scattering. Hlinka et al. foundthat the DS in 1−xPZN−xPT with x=0.08 is truly elastic,with any dynamics being slower than 8 GHz.11 This resultcontrasts with those obtained by neutron scattering fromPMN and 1−xPMN−xPT x=0.32 where the QE compo-nent has a lifetime varying between 0.05 and 0.2 THz as afunction of the temperature,6–9 as well as results from Bril-louin experiments in 1−xPZN−xPT.12In this letter we present neutron scattering results ob-tained in 1−xPZN−xPT with x=0.07. We show that thelow-energy part of the excitation spectrum contains in addi-tion to the elastic DS observed by Hlinka et al. a QE com-ponent that was not reported before. We present an analysisof the evolution of the intensity and of the linewidth of thiscomponent as a function of the temperature and compare theresults with those obtained in 1−xPMN−xPT x=0 andx=0.32.8,9We used the cold neutron three-axis spectrometer TASPRef. 14 SINQ,15 PSI operated in the constant kf-modewith kf =1.64 Å−1. A PG filter was installed in the scatteredbeam to reduce contaminations by higher-order wavelengths.aElectronic mail: gelu.rotaru@psi.ch.APPLIED PHYSICS LETTERS 93, 032903 20080003-6951/2008/933/032903/3/$23.00 © 2008 American Institute of Physics93, 032903-1Downloaded 01 Dec 2009 to 130.158.56.186. Redistribution subject to AIP license or copyright; see http://apl.aip.org/apl/copyright.jspThe horizontal collimation was 10 /Å−80−80−80. Withthat setting the energy resolution was 0.26 meV. The sample1 cm3 in volume was mounted in a standard furnace withthe 110 cubic axis vertical. Both constant-Q and constant-energy scans were performed around the 1 1 0 Bragg re-flection in the temperature range 300 KT630 K. Figure1a shows a typical energy scan performed at T=630 K andQ = 1,1,0.075. The spectrum consists of a transverse acous-tic TA phonon and of scattering centered around the elasticposition. The incoherent scattering was measured at hightemperature at Q = 1,1,0.3 and subtracted from the data.Figure 1b shows the same scan at T=425 K, i.e., close tothe phase transition to the ferroelectric state. At this tempera-ture the neutron intensity measured around the elastic posi-tion has strongly increased. The lineshape of the TA phononis well described by a damped-harmonic-oscillator functionconvoluted with the resolution function of the spectrometer.We obtain for the TA dispersion TA=d sinq, withd=6.80.1 meV. It turns out from the analysis of the data atall temperatures that the central component cannot be repro-duced by a resolution-limited Gaussian function only andconsists of two components, the truly elastic diffuse scatter-ing observed by Hlinka et al.11 and QE scattering. The QEscattering is modeled by a Lorentzian function as was donebefore in PMN Refs. 6–8 and 1−xPMN−xPT.9QE ,q,T =0,T1 + q/2qq2 + 2, 1where q=0+Dq2. We find that D=181 meV Å2 in1−xPZN−xPT x=0.07. =1 / is the inverse of the cor-relation length  and is obtained from constant energy scans.Figure 2 shows the temperature dependence of T and0T, 0.120.01 Å−1 at 630 K, and decreases with de-creasing temperature as does the linewidth of the QE scatter-ing: 0=0.480.01 meV at T=630 K and 0.210.01 meVbelow 475 K, where the dynamics of the PNRs freeze. Asimilar behavior is observed for the temperature dependenceof the width of the CP in light scattering where080 GHz 0.3 meV in the ferroelectric phase.12 On theother hand, the intensity of the elastic part of the diffusescattering increases strongly below 600 K and reaches amaximum around Tc, as shown in Fig. 3. The temperaturedependence of the susceptibility of the QE scattering isshown in Fig. 4. 0,T increases strongly on cooling below630 K, reaches a maximum around Tc, and decreases rapidlyin the ferroelectric phase. The temperature dependence of thesusceptibility of the QE scattering in 1−xPZN−xPTx=0.07 as a similar temperature dependence as the dielec-tric permittivity like in 1−xPMN−xPT x=0, 0.32.To conclude, we found that in 1−xPZN−xPTx=0.07 the DS consists of two components associated withtwo different timescales, which reconciles the discrepancybetween light scattering12 and previous neutron scatteringmeasurements.11 We have also shown that the temperaturedependences of the CP and QE components have a similarbehavior in both 1−xPMN−xPT and 1−xPZN−xPTFIG. 1. Typical const-Q scans at T=630 K a and at T=425 K b. Thesolid line is the fit. The bold line emphasizes the contribution of the QEcomponent.FIG. 2. The temperature dependences of the damping of the QE scattering0 and of the inverse correlation length .FIG. 3. The temperature dependences of the elastic component of the dif-fuse scattering.032903-2 Rotaru et al. Appl. Phys. Lett. 93, 032903 2008Downloaded 01 Dec 2009 to 130.158.56.186. Redistribution subject to AIP license or copyright; see http://apl.aip.org/apl/copyright.jspx=0.07, which brings further evidence that the static com-ponent corresponds to atomic displacements that form thePNR and the QE scattering to the dynamics of the PNR, asdiscussed in Refs. 6–10.The authors thank R. A. Cowley for discussions. Thiswork was performed at the spallation neutron source SINQ,Paul Scherrer Institut, Villigen Switzerland and was par-tially supported by the Swiss National Foundation ProjectNo. 20002-111545.1V. A. Shuvaeva, A. M. Glazer, and D. Zekria, J. Phys.: Condens. Matter17, 5709 2005.2J. J. Lima-Silva, I. Guedes, J. Medes Filho, A. P. Ayala, M. H. Lente, J. A.Eiras, and D. Garcia, Solid State Commun. 131, 111 2004.3G. Burns and F. H. Dacol, Solid State Commun. 48, 853 1983.4M. Roth, E. Mojaev, E. Dul’kin, P. Gemeiner, and B. Dkhil, Phys. Rev.Lett. 98, 265701 2007.5I.-K. Jeong, T. W. Darling, J. K. Lee, Th. Proffen, R. H. Heffner, J. S.Park, K. S. Hong, W. Dmowski, and T. Egami, Phys. Rev. Lett. 94,147602 2005; W. Dmowski, S. B. Vakhrushev, I.-K. Jeong, M. P.Hehlen, F. Trouw, and T. Egami, ibid. 100, 137602 2008.6S. N. Gvasaliya, S. G. Lushnikov, and B. Roessli, Phys. Rev. B 69,092105 2004.7H. Hiraka, S.-H. Lee, P. M. Gehring, G. Xu, and G. Shirane, Phys. Rev. B70, 184105 2004.8S. N. Gvasaliya, B. Roessli, R. A. Cowley, P. Huber, and S. G. Lushnikov,J. Phys.: Condens. Matter 17, 4343 2005.9S. N. Gvasaliya, B. Roessli, R. A. Cowley, S. Kojima, and S. G. Lushni-kov, J. Phys.: Condens. Matter 19, 016219 2007.10C. Stock, R. J. Birgeneau, S. Wakimoto, J. S. Gardner, W. Chen, Z. G. Ye,and G. Shirane, Phys. Rev. B 69, 094104 2004.11J. Hlinka, S. Kamba, J. Petzelt, J. Petzelt, J. Kulda, C. A. Randall, and S.J. Zhang, J. Phys.: Condens. Matter 15, 4249 2003.12F. Jiang and S. Kojima, Ferroelectrics 266, 19 2002; J.-H. Ko, D. H.Kim, and S. Kojima, Phys. Rev. B 77, 104110 2008.13Y. Hosono, K. Harada, T. Kobayashi, K. Itsumi, M. Izumi, Y. Yamashita,and N. Ichinose, Jpn. J. Appl. Phys., Part 1 41, 7084 2002.14F. Semadeni, B. Roessli, and P. Böni, Physica B 297, 152 2001.15W. E. Fischer, Physica B 234–236, 1202 1997.FIG. 4. The temperature dependences of the susceptibility 0,T of the QEscattering and of the dielectric constant 	 taken from Ref. 13.032903-3 Rotaru et al. Appl. Phys. Lett. 93, 032903 2008Downloaded 01 Dec 2009 to 130.158.56.186. Redistribution subject to AIP license or copyright; see http://apl.aip.org/apl/copyright.jsp

Evolution of the neutron quasielastic scattering through the ferroelectric phase transition in 93%PbZn1/3Nb2/3O3–7%PbTiO3

Evolution of the neutron quasi-elastic scattering through the
  ferroelectric phase transition in 93%PbZn$_{1/3}$Nb$_{2/3}$O$_3$ - 7%
  PbTiO$_3$

Evolution of the neutron quasi-elastic scattering through the ferroelectric phase transition in 93%PbZn $_{1/3}$ Nb $_{2/3}$ O $_3$ - 7% PbTiO $_3$

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Evolution of the neutron quasi-elastic scattering through the ferroelectric phase transition in 93%PbZn1/3_{1/3}1/3​Nb2/3_{2/3}2/3​O3_33​ - 7% PbTiO3_33​

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Evolution of the neutron quasi-elastic scattering through the ferroelectric phase transition in 93%PbZn $_{1/3}$ Nb $_{2/3}$ O $_3$ - 7% PbTiO $_3$