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International audience; Magnetic phase transition temperature of the PbFe1/2Nb1/2O3 (PFN) nanofilm on the SrTiO3 substrate was reported to be about 50 K higher than that in the bulk samples. We carried out comparative Raman studies of a 90 nm-thick PFN epitaxial film on SrRuO3-buffered (001) SrTiO3 substrate and the bulk samples of ceramic PFN and a single crystal. It was found out that the bands at approximate to 250 cm(-1) and approximate to 700 cm(-1) in the spectrum of the film, corresponding to Fe-O vibrational modes, are shifted by about 20 cm(-1) to higher frequencies as compared to the bulk samples. This result is in line with the predictions of the recent first-principles calculations that compressive misfit strain stimulates the disorder in the Fe and Nb distribution in the lattice, leading to an increase of the magnetic phase transition temperature. Such disordering might cause the changes in the Fe-sublattice of PFN seen in the Raman spectrum. (C) 2016 Elsevier B.V. All rights reserved.

International audience; In ferroelectric thin films, controlling the orientation of the polarization is a key element to controlling their physical properties. We use laboratory and synchrotron X-ray diffraction to investigate ferroelectric bicolor PbTiO3/PbZr0.2Ti0.8O3 and tricolor PbTiO3/SrTiO3/PbZr0.2Ti0.8O3 superlattices and to study the role of the SrTiO3 layers on the domain structure. In the tricolor superlattices, we demonstrate the existence of 180° ferroelectric stripe nanodomains, induced by the depolarization field produced by the SrTiO3 layers. Each ultrathin SrTiO3 layer modifies the electrostatic boundary conditions between the ferroelectric layers compared to the corresponding bicolor structures, leading to the suppression of the a/c polydomain states. Combined with the electrostatic effect, the tensile strain induced by PbZr0.2Ti0.8O3 in the PbTiO3 layers leads to polarization rotation in the system as evidenced by grazing incidence X-ray measurements. This polarization rotation is associated with the monoclinic Mc phase as revealed by the splitting of the (HHL) and (H0L) reciprocal lattice points. This work demonstrates that the tricolor paraelectric/ferroelectric superlattices constitute a tunable system to investigate the concomitant effects of strains and depolarizing fields. Our studies provide a pathway to stabilize a monoclinic symmetry in ferroelectric layers, which is of particular interest for the enhancement of the piezoelectric properties.

We have synthesized [Pb(Mg1/3Nb2/3)O-3]((1-x)Lambda)/[PbTiO3](x Lambda) (PMN(1-x)LambdaPT(x)Lambda) super-lattices by pulsed laser ablation onto MgO substrates buffered with La1/2Sr1/2CoO3 (LSCO). We varied the composition (0.1

We have performed x-ray diffraction and Raman spectroscopy measurements in the temperature range of 300–873 K on a single phase epitaxially oriented BaTiO3 thin film grown by pulsed laser deposition on a single crystal MgO substrate. The θ–2θ room temperature diffraction measurements and asymmetric rocking curves indicate that the film is very weakly tetragonal with the c-axis parallel to the plane of the film. X-ray diffraction measurements up to high temperature reveal only a change in slope in the perpendicular to the plane lattice parameter around 450 K (in bulk Tc=395 K) indicating that a diffuse-like of phase transition is taking place. Room temperature polarized Raman spectra show that the film is indeed tetragonal with C4v symmetry and with the a-axis perpendicular to the film plane. Monitoring of the overdamped soft mode and the 308 cm−1 mode confirms that the phase transition is taking place over a wide temperature range according to the x-ray results. The increase of the phase transition temper...

We investigate the ferroelectric phase transition and the domain formation in a periodic multilayer structure consisting of alternate ferroelectric (FE) and paraelectric (PE) layers of nanometric thickness. The principle result of this study is that the polarization domains formed in the different FE layers interact with each other through the PE layers via an inhomogeneous depolarizing electric field emerging from the domains of the neighboring FE layers. We call this a proximity effect. Based on electrostatic equations coupled with those obtained by the minimization of the Ginzburg-Landau functional for a ferroelectric, we calculated the renormalization of T c as a function of the FE/PE superlattice modulation period. We can describe quantitatively the recent experiments on the thickness dependence of the ferroelectric transition in KNbO 3 -KTaO 3 strained-layer superlattices.

We present structural results on Pb(Mg 1/3 Nb 2/3 )O 3 (PMN) thin films grown by pulsed laser deposition (PLD). Reflection high energy electron diffraction (RHEED), room temperature θ-2θ and phi scan x-ray diffraction measurements indicate that the films are epitaxially oriented. We have performed x-ray diffraction measurements as a function of temperature (10 K < T < 900 K) on two PMN films, 1500 A and 7000 A thick, grown on (100) MgO substrates buffered with La 1/2 Sr 1/2 CoO 3 (LSCO). We compare the temperature dependent evolution of the film's out of plane lattice parameter with that of single crystal PMN. At first sight the dependencies are markedly different but can be explained by taking into account the thermal expansion of the MgO substrate. Asymmetric rocking curves taken about the {303} families of planes indicate that the substrate induces a tetragonal distortion in the films which exists over the entire temperature range investigated.

X-ray diffraction and Raman spectroscopy were used to examine the structure and the ferroelectric state of highly oriented barium titanate thin film deposited by the pulsed laser deposition on (001)MgO substrate. It is found that the film is weakly tetragonal and domains are a-axis oriented. The temperature dependencies of the out plane lattice parameter and the tetragonal Raman peak at 308 cm m 1 show that the ferro-paraelectric phase transition occurs above the the bulk transition temperature and can be considered as diffuse. This behaviour is attributed to the stress effect.

We report the results of an electron spin resonance study of Ti3+ centres in SrTiO3 single crystals. The Ti3+ centres are created in perturbed regular Ti4+ sites by trapping a photoelectron from the conduction band after ultraviolet irradiation of the sample at low temperature (T Tc (Tc ≈ 105 K corresponds to the temperature of the cubic–tetragonal phase transition), the Ti3+ centre exhibits an orthorhombic symmetry of the g-tensor with its principal axes oriented exactly along 001 and 110 crystal directions: g[110] = 1.9920, g[10] = 1.9375, g[001] = 1.8843. At T < Tc, due to a structural phase transition, two of the Ti3+ principal axes are tilted relative to the 110 directions by up to ±8o in the (001) crystal plane. The spectroscopic data are explained assuming Jahn–Teller orthorhombic distortions of the oxygen octahedron with non-linear T2g × (eg + t2g) vibronic coupling.

The elastic properties of both polycrystalline and epitaxial PbTiO3 (PTO) thin films are studied using Brillouin scattering spectroscopy. The epitaxial PTO films were prepared by pulsed laser ablation on (1) a [0 0 1] single crystal of SrTiO3 (STO) doped with Nb and (2) a [0 0 1] STO buffered with a layer of YBa2Cu3O7. The polycrystalline PTO films were prepared by sol–gel on a Si substrate buffered with TiO2 and Pt layers. The data analysis takes into account the ripple and the elasto-optic contributions. The latter significantly affects the measured spectra since it gives rise to a Love mode in the p–s scattering geometry. At room temperature, the spectra of the epitaxially grown samples are interpreted using previously published elastic constants of PTO single crystals. Sol–gel samples exhibit appreciable softening of the effective elastic properties compared to PTO single crystals: this result is explained by taking into account the random orientation of the microscopic PTO grains. For both the polycrystalline and the epitaxial films we have determined that the piezoelectric terms do not contribute to the spectra. The temperature dependence of the spectra shows strong anomalies of the elastic properties near the ferroelectric phase transition. Compared to the bulk, TC is higher in the sol–gel films, while in the epitaxial films the sign of the TC shift depends on the underlying material.

Ferroelectric PbTiO3(PTO)/BaTiO3(BTO) superlattices have been grown on SrTiO3 buffered MgO substrates by laser ablation. An extended X-ray study has shown that the orientation of individual layers is c-domain (i.e., c-axis of the tetragonal phase perpendicular to the substrate) for BTO and a-domain for PTO, contrary to what is observed for single PTO or BTO thin films, which are both c-oriented. Raman scattering reinforces this assertion, and also defines the critical modulation period A above which stress relaxation occurs via misfit dislocations. Confined modes have been also observed, in the same way as in semiconductor superlattices. The temperature variation of the soft mode frequency is shown to depend upon A.

It is reported the results of ESR study of Ti3+ centers in SrTiO3 single crystals. The Ti3+ centers are created in perturbed regular Ti4+ sites by trapping of a photoelectron from the conduction band after ultraviolet (UV) irradiation of the sample at low temperature (T Tc (Tc ≈ 105 K corresponds to the temperature of the cubic-tetragonal phase transition) Ti3+ center exhibits orthorhombic symmetry of g-tensor with its principal axis oriented exactly along crystal directions. Orthorhombic symmetry of the center is atributed to a Jahn-Teller T2gX(eg+t2g) nonlinear couling stabilized by Ca(Ba) impurities on two Sr-sites. At T directions on the angle of ± 8° in (001) crystal plane.

A thermodynamic theory for the calculation of static and dynamic polarization profiles of ferroelectric thin film multilayers is developed. The free energy functional is written down using a multilayer model in which c-domain layers of the ferroelectric material alternate with a-domain layers of a second ferroelectric materials. We assume that the interfaces are perfectly sharp and that the polarization at these boundaries is zero. The equilibrium polarization profile, its temperature and thickness dependencies were determined from the solutions of the Euler-Lagrange equations. A thickness induced ferroelectric phase transition is shown to exist and its transition temperature and critical layer thickness depend on the domains orientation. The equation determining the time and space dependence of the polarization is proposed and solved. The calculated dispersion law for the nonlinear polarization waves in multilayer structures reveals a critical wave vector or a critical layer thickness, for which...

A thermodynamic theory of dielectric response in ferroelectric thin film multilayers is developed. The solution of Lame equation for static dielectric susceptibility has shown that susceptibility diverges at the transition temperature of the thickness induced ferroelectric phase. This divergence is shown to be the origin of the giant dielectric response observed in some multilayers. The theory gives an excellent fit to the temperature dependence of the giant susceptibility observed recently in multilayers of PbTiO3-Pb1-xLaxTiO3 (x = 0.28).

We have performed X-ray diffraction and Raman spectroscopy on three PbTiO 3 /BaTiO 3 superlattices (PTO/BTO) from room temperature (RT) to 600°C. The superlattices were 4000 A thick and the modulation wavelengths Λ, with equally thick layers of PTO and BTO, were 136, 187 and 357 A. The samples were laser deposited onto single crystal MgO substrates buffered with 50 A of SrTiO 3 (STO). We observe no X-ray evidence of a phase transition in the PTO layers of these three superlattice samples up to 600°C. This result was reinforced by X-ray modeling of the samples. We also monitored the E(1TO) or “soft “ mode by Raman spectroscopy up to 550°C and found only a linear decrease of mode frequency with temperature for all three superlattices: another sign that no phase transition is taking place in this temperature range.

We have used pulsed laser ablation to grow a series of PbTiO3/BaTiO3 (PTO/BTO) multilayers with a modulation wavelength Λ that varies between 50A

We have used laser ablation to grow series of ${\mathrm{PbTiO}}_{3}{/\mathrm{B}\mathrm{a}\mathrm{T}\mathrm{i}\mathrm{O}}_{3}$ (PTO/BTO) multilayers with a modulation wavelength \ensuremath{\Lambda} that varies between $50\AA{}l\ensuremath{\Lambda}l360\AA{}.$ Modeling the x-ray-diffraction patterns of the multilayers indicates that the PTO layers are a-axis oriented. The Raman measurements reinforce this interpretation. The soft-mode Raman line shifts abruptly in frequency above $\ensuremath{\Lambda}=240\AA{}$ due to possible strain relaxation of the multilayer, and the \ensuremath{\Lambda} dependent position of an asymmetric line in the vicinity of 200 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ is modeled as a confined mode, a signature of a modulated structure.

We have successfully grown in situ, by laser ablation, the following heterostructures: Pb(Zr0.52Ti0.48)O3 / YBa2Cu3O7 / CeO2 / (1102) Al2O3(PZT/YBCO/CeO2/Al2O3), Pb(Zr0.52Ti0.48)O3 / YBa2Cu3O7 / (100) SrTiO3(PZT/YBCO/STO), and Pb(Zr0.52Ti0.48)O3 / SrTiO3 / (100) MgO (PZT/STO/MgO). By combining RHEED. x-ray diffraction and atomic force microscopy, we have determined that (a) all the buffer and electrode layers are atomically flat, (b) PZT grows in the 2D to 3D Stransky-Krastanov mode, (c) there is an epitaxial relationship between the in-plane axes of the layers and the substrates, and (d) the c-axis of PZT is perpendicular to the plane of the film. Raman scattering shows a significant difference in spectra between a PZT thin film heterostructure and a ceramic PZT target. This is further evidence for the epitaxial nature of the PZT films and their fundamental difference with respect to ceramic samples.

International audience; We report a comparative Raman study of 0.65(PbMg1/3Nb2/3O3)-0.35(PbTiO3) (PMN-0.35PT) single crystal and thin film. Raman spectra investigation indicates a change in bulk from the high temperature cubic to the tetragonal phase and then to the low temperature Mc monoclinic phase. The transition temperatures are in good agreement with the ones previously observed by dielectric measurements on the same sample. In contrast, we observe no phase transition to the monoclinic phase in the PMN-0.35PT 4000 ˚A thick film and only a cubic to tetragonal diffuse transition has been determined at high temperature. The enhanced stability of the tetragonal phase and the absence of low temperature monoclinic phase have been attributed to the in plane strain.

International audience; Ferroelectric symmetric superlattices consisting of alternating layers of PbTiO3 and PbZr0.2Ti0.8O3, were grown by pulsed laser deposition on SrTiO3 and SrRuO3-coated SrTiO3 substrates. The superlattices, with wavelengths K ranging from 20A ° to 200A ° , were analyzed using x-ray diffraction (h 2h diffraction scans, rocking curves, and reciprocal space mapping), high resolution transmission electron microscopy, and piezoforce scanning microscopy. For large-period superlattices, the strain is relieved by the formation of an a/c polydomain structure which propagates through the whole film. We investigate the influence of the wavelength on the a-domain volume fraction, the lattice parameters, the in-plane strain exx, and the mosaicity of the samples. We show that with decreasing the wavelength, a reduction of the a-domain volume fraction is observed as well as a reduced tensile in-plane strain and a lower mosaicity. A concomitant improvement of the local ferroelectric response is detected. Below a critical wavelength of about 30A ° and a critical sample thickness of 500A ° , the formation of 90 a/c domains is inhibited and the superlattices are completely c oriented. Thus the reduced wavelength induces compressive strain which dominates over the tensile clamping due to the thermal expansion mismatch between the substrate and the superlattice. This compressive strain favors a c-oriented structure in the PbTiO3/PbZr0.2Ti0.8O3 superlattices.

International audience; We report a temperature-dependent high-resolution X-ray diffraction investigation of 200nm epitaxial BiFeO3 thin films grown on (001) SrTiO3. We were successful in making epitaxial thin films thermally stable, a key requirement for this study. Our results provide evidence that BiFeO3 undergoes three ghtemperature transitions: an antiferromagnetic transition at 425 C, a first-order - phase transition between 745 C and 780 C and a smoother transition toward the -phase at 860 C. Both the - and - transitions take place 60 C lower than the bulk values whereas the antiferromagnetic transition occurs 55 C higher. This underscores the part played by strain and also emphasizes that BiFeO3 is not a conventional ferroelectric perovskite. Reciprocal space maps reveal the unusual result that the thin films remain monoclinic on crossing the - phase transition. Linear extrapolation of the in-plane lattice parameters to higher temperatures rules out cubic symmetry for the -phase.

International audience; We used pulsed laser deposition to grow a series of PbTiO3/PbZr0.2Ti0.8O3 superlattices on SrTiO3 and SrRuO3/SrTiO3 substrates. An a/c polydomain structure was evidenced by reciprocal space mapping and by transmission electron microscopy. Insertion of ultra-thin layers of SrTiO3 at the interfaces between PbTiO3 and PbZr0.2Ti0.8O3 layers has inhibited this polydomain formation. A strong decrease in the tetragonality indicates clearly that the polarization state in these superlattices has changed due to the insertion of the SrTiO3 layers. A purely elastic mechanism does not seem to explain the determined structural parameters

Elastic and specific-heat measurements have been performed on single-phase polycrystalline ${\mathrm{Y}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ca}}_{\mathit{x}}$${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{4}$${\mathrm{O}}_{8}$ (x=0, 0.025, 0.05, 0.1) in the temperature region from 100 to 180 K. Anomalies are detected in elastic and specific-heat measurements at 150 K for Ca-doped specimens. A reversible steplike change in sound velocity accompanied by an attenuation peak is observed in material with x=0.1 doping at 150 K on cooling and heating, for both longitudinal and transverse modes. These elastic anomalies have a clearly observable counterpart in the specific heat. The anomalies in elastic and specific-heat measurements show dominantly the character of a mean-field-type phase transition. We observe similar anomalies at the same temperature even for x=0.025 and 0.05, while for pure ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{4}$${\mathrm{O}}_{8}$ samples no anomalies are found in this temperature region. Thus we find a Ca-induced, but concentration-independent, transition temperature in the available range of x values. No magnetic anomaly is found by ac magnetic susceptibility. The transition is proposed to be of a structural type although x-ray powder diffraction did not reveal the origin.

We have measured the a.c. magnetic permeability response function μ = μ′ + iμ″ in melt-processed melt-grown YBa2Cu3O7 with Y2BaCuO5 inclusions (MPMG) and in single crystal YBa2Cu3O7 (SC) in magnetic fields of up to 8 T oriented either parallel or perpendicular to the crystalline c-axis. The lossy part of the permeability μ″ (H,T) is used to probe the flux dynamics in the vicinity of the irreversibility line. For H | c, the MPMG has a higher irreversibility temperature Tirr(H) than the SC sample, while for H ⊥ c, Tirr(H) is similar for both samples. Because of the strong Hac dependence and the weak frequency dependence of μ″ (H,T) for H ⊥ c, we contend that the vortex system is in the glass phase. For H | c, the Hac dependence of μ″ is weak and its frequency dependence is strong, indicating that here the system is much closer to the glass/liquid transition. For the SC sample with H ⊥ c, μ″ (T) exhibits an anomalous structure which appears only in finite applied d.c. fields and disappears at fields greater than 1.5 T.

We report a temperature-dependent high-resolution x-ray diffraction investigation of 200-nm epitaxial BiFeO3 thin films grown on (001) SrTiO3. We find that BiFeO3 undergoes two high-temperature transitions: a first-order alpha-beta phase transition between 745 and 780 degrees C and a more diffuse transition toward the gamma phase at 860 degrees C. Reciprocal space maps reveal that thin films remain monoclinic crossing the alpha-beta phase transition. Linear extrapolation of the in-plane lattice parameters to higher temperatures appears to rule out cubic symmetry for the gamma phase.

Epitaxial NaNbO3 thin films have been grown by pulsed laser deposition on cubic (00l) MgO substrate with epitaxial (La0.5Sr0.5)CoO3 buffer layer. Micro-Raman spectroscopy studies revealed that the ferroelectric Q phase (Pmc21, Z=4) is stable in a 250-nm-thick film in contrast to the antiferroelectric phase P (Pbma, Z=8) known to exist in the bulk single crystals and ceramics of undoped stoichiometric NaNbO3. Temperature-dependent Raman spectra indicate that the Q phase is stable over a wide temperature range (at least from 80 to 600 K), while the low-temperature ferroelectric rhombohedral phase N, typical for NaNbO3 single crystals, is not observed.

We have measured the ac magnetic permeability response function μ = μ' + iμ'' in melt-processed melt grown YBa2Cu3O7 with Y2BaCuO5 inclusions (MPMG) and in single crystal YBa2Cu3O7 (SC) in applied magnetic fields up to 8 Tesla oriented either parallel or perpendicular to the crystalline c-axis. The ac response of the two samples has been mapped out as a function of temperature, frequency, ac field amplitude, dc applied field, and field orientation. The peak in the lossy part of the susceptibility μ'' is used to probe the flux dynamics in the vicinity of the irreversibility line. The data are interpreted by comparison with expectations for an anisotropic vortex glass-to-liquid transition. The inferred melting lines as well as the frequency dependence and non-linear response are in overall agreement with the expected behavior. In the range of available parameters and variables we find the system to be in the solid vortex phase for H⊥c since there is a strong Hac dependence and only a weak frequency dependence on the temperature position of the loss peak. For H||c, the situation is reversed, and the loss peak depends only weakly on Hac and strongly on the frequency.

We present electric and magnetic properties of 0.8Pb(Fe1/2Nb1/2)O3-0.2Pb(Mg1/2W1/2)O3 films epitaxially grown on (001) SrTiO3 substrates using pulsed laser deposition. A narrow deposition window around 710 oC and 0.2 mbar has been identified to achieve epitaxial single-phase thin films. A typical Vogel-Fulcher relaxor-like dielectric and magnetic susceptibility dispersion is observed, suggesting magnetoelectric relaxor behavior in these films similar to the bulk. We determine a magnetic cluster freezing temperature of 36 K, while observing weak ferromagnetism via magnetic hysteresis loops up to 300 K., 12 pages, 4 figures

We have grown lead iron niobate thin films with composition Pb(Fe1/2Nb1/2)O3 (PFN) on (0 0 1) SrTiO3 substrates by pulsed laser deposition. The influence of the deposition conditions on the phase purity was studied. Due to similar thermodynamic stability spaces, a pyrochlore phase often coexists with the PFN perovskite phase. By optimizing the kinetic parameters, we succeeded in identifying a deposition window which resulted in epitaxial perovskite-phase PFN thin films with no identifiable trace of impurity phases appearing in the X-ray diffractograms. PFN films having thicknesses between 20 and 200 nm were smooth and epitaxially oriented with the substrate and as demonstrated by RHEED streaks which were aligned with the substrate axes. X-ray diffraction showed that the films were completely c-axis oriented and of excellent crystalline quality with low mosaicity (X-ray rocking curve FWHM, 13 Pages, 6 figures. To be published in J. Mag. Mag Mater. proceedings of EMRS2008

We have used pulsed laser deposition to grow BiFeO3/BaTiO3 multilayers on SrTiO3 substrates. The samples are characterized by Reflection High Energy Electron Diffraction (RHEED), Atomic Force Microscopy (AFM), and by X-ray diffraction measurements and modelling. The two multilayers investigated here have modulation periods A = 90A and 180A, while the total thickness of 1800A is the same for both samples. Hence, twice as many interfaces are encountered for the A = 90A than for the A = 180A sample. SQUID magnetometer measurements performed on these multiferroic samples show that the magnetization is significantly larger for the smaller wavelength sample thus pointing to a multilayer effect between the magnetic susceptibility and the number of interfaces per unit volume.

We have used x-ray diffraction and Raman spectroscopy over a broad temperature range $(90\phantom{\rule{0.3em}{0ex}}\mathrm{K}\ensuremath{\leqslant}T\ensuremath{\leqslant}900\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ to study the structural and dynamical behavior of ${[{\mathrm{PMN}}_{(1\ensuremath{-}x)\ensuremath{\Lambda}}∕{(\mathrm{Pb}\mathrm{Ti}{\mathrm{O}}_{3})}_{x\ensuremath{\Lambda}}]}_{10}$ superlattices $(x=0.2,0.5,0.8)$ (where PMN is $\mathrm{Pb}{\mathrm{Mg}}_{1∕3}{\mathrm{Nb}}_{2∕3}{\mathrm{O}}_{3}$), which were epitaxially grown with a nominal wavelength $\ensuremath{\Lambda}$ of $130\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ by pulsed laser deposition on MgO substrates buffered with ${\mathrm{La}}_{0.5}{\mathrm{Sr}}_{0.5}\mathrm{Co}{\mathrm{O}}_{3}$. We present a comparison of the results obtained on these superlattices with the temperature evolution of three fictitious superlattices constructed using the temperature-dependent data obtained on individual $\mathrm{Pb}\mathrm{Ti}{\mathrm{O}}_{3}$ and $\mathrm{Pb}{\mathrm{Mg}}_{1∕3}{\mathrm{Nb}}_{2∕3}{\mathrm{O}}_{3}$ epitaxial thin films. From this study, we conclude that the PMN layers in superlattices retain the structural characteristics, including the tetragonal distortion, of relaxor thin films. The $\mathrm{Pb}\mathrm{Ti}{\mathrm{O}}_{3}$ layers exhibit in-plane polar orientation at all temperatures. X-ray diffraction shows the stabilization, due to biaxial stress, of the ferroelectric order up to at least $873\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in the $\mathrm{Pb}\mathrm{Ti}{\mathrm{O}}_{3}$ layers (${T}_{C}=763\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in bulk). The tetragonal symmetry and ferroelectric order of the $\mathrm{Pb}\mathrm{Ti}{\mathrm{O}}_{3}$ layers, as well as the relaxorlike behavior of the PMN layers, are confirmed by Raman spectroscopy.

We used pulsed laser deposition to grow a series of BaTiO3 /2 / BaTi0.68Zr0.32O3 /2 BTZ/BT superlattices SL’s with a modulation period that varies between 16 A 1008 A; the total thickness is kept constant at about 4000 A. We determine the out-of-plane lattice parameters of the SL constituents by modeling the x-ray diffractograms of the SL’s. The results indicate that the polar c axis of the BT layers lies in the plane of the film. The Raman data reinforces this interpretation. The Raman spectra of SL’s give evidence of coupling between BT and BTZ layers and a narrowing of the Raman peaks suggest a reduction of the disorder of the Ti4+ ions due to the strain. This strain resulting from the lattice mismatch between the constituent layers is responsible for the upward frequency shift of the soft modes, especially the E 1TO mode, which is markedly altered with respect to its analogs in BT-bulk crystals and BT film. This soft-mode behavior as a function of indicates that the crystal structure of all SL’s is more rigid than in BTZ and BT single thin films.

We investigate the ferroelectric phase transition and domain formation in a periodic superlattice consisting of alternate ferroelectric (FE) and paraelectric (PE) layers of nanometric thickness. We find that the polarization domains formed in the different FE layers can interact with each other via the PE layers. By coupling the electrostatic equations with those obtained by minimizing the Ginzburg-Landau functional we calculate the critical temperature of transition Tc as a function of the FE/PE superlattice wavelength and quantitatively explain the recent experimental observation of a thickness dependence of the ferroelectric transition temperature in KTaO3/KNbO3 strained-layer superlattices., Latest version as was published in PRL

We have grown a series of [PbMg1/3Nb2/3O3]((1-x)Lambda)/[PbTiO3](xLambda)(PMN1-x/PTx) superlattices for which the composition varies, 0.1less than or equal toxless than or equal to0.8, but the modulation period Lambda is kept constant at about 130 A. X-ray diffraction indicates that the polar c axis of the PT layers lies in the plane of the films. The Raman spectra, which reflect the sum of the spectra of PMN and the PT layers, confirm the a-domain orientation of the PT layers. A downshift of the E(1TO) soft mode of the PT layers was attributed to tensile stress, estimated to be in the range of 2.5-3.6 GPa, induced by the lattice mismatch of PMN/PT layers. We observe the splitting of the "silent" mode in PT into distinct modes B-1 and E and attribute this to the strains present in the layers.

We have used a standard Weissenberg camera in the oscillating mode to characterize the in‐plane structure of YBa2Cu3O7 thin films. We find that for films optimally grown on (100) MgO or (100) SrTiO3 substrates, the in‐plane film axes are aligned parallel to the substrate axes. This is true both for solely c‐axis oriented films (perpendicular to the film plane) and for mixed a‐ and c‐axis oriented films. For a film grown on (110) SrTiO3, we have established that the film orientation perpendicular to the film plane is solely (103) and not (110) or a mixture of the two. In addition the in‐plane film axes are colinear to the substrate axes.

We present the dielectric dispersion in a Pb(Fe1/2Nb1/2)O3 (PFN) thin film grown on (001) SrTiO3 substrate from 20 MHz to 20 GHz in the temperature range of 270 to 340 K. In the radio frequency region, the hopping charge transport and associated polar nanoregion and/or domain-wall motion contribute to the spectrum. In the microwave region, relaxational dispersion was observed with a dielectric contribution of Δe ≈ 600 at room temperature having a characteristic frequency (fm)0.4 = 9.8 · (T−T0) Hz, where T0 is 660 K. It is associated with possible mode-softening behavior, related to the onset of polar nanoregions at T0. The dielectric permittivity shows similarities with 1-dimensional Ising model behaviour.

We have measured the ac magnetic permeability μ in YBa2Cu3O7 with Y2BaCuO5 inclusions and in single crystal YBa2Cu3O7, in applied magnetic fields parallel and perpendicular to the c-axis. We find that the inclusions act as strong pinning sites when H❙c, but have a deleterious effect on the superconductor when H⊥c.

We have made magnetization and x-ray diffraction measurements on an epitaxial Pb(Fe1/2Nb1/2)O3 200 nm film. From the temperature dependence of the out-of-plane lattice parameter we can assign a Burns' temperature at Td ~ 640 K, a temperature at T* ~ 510 K, related to the appearance of static polar nanoregions, and an anomaly occurring at 200 K. The latter is precisely the N\'eel temperature TN determined from magnetization and points to spin-lattice coupling at TN ~ 200 K. We also observe "weak ferromagnetism" up to 300K and propose superantiferromagnetic clusters as a plausible scenario to explain this hysteresis above TN., Comment: 12 pages, 4 figures

The principle of operation of the “Laves-Ernst” compensator in polarized reflected light is explained and illustrated by means of the contrast generated between large and lamellar orthorhombic domains of single crystals and epitaxial layers of YBa2Cu3O7-δ (“YBCO”).

We have fabricated epitaxial thin films of the relaxor Pb(Mg 1/3 Nb 2/3 )O 3 (PMN) and multilayer structures of relaxor/ferroelectric Pb(Mg 1/3 Nb 2/3 )O 3 /PbTiO 3 (PMN/PTO) using pulsed laser deposition. We present results obtained using reflection high energy electron diffraction (RHEED), x-ray diffraction (XRD) and transmission electron microscopy (TEM) on thin films of PMN grown on single crystal (100) SrTiO 3 substrates using a stoichiometric PMN ceramic target and a PMN-2%Mg target. With the latter target we were able to produce pyrochlore free thin films. RHEED images 140A PMN films consist of sharp lines and Kikuchi bands which indicate smooth surfaces. This is borne out by the observation of XRD Laue (thickness) oscillations. TEM images of PMN films with some pyrochlore show the PMN growth is columnar and the widths are on the order of 400A. Multilayer structures of(PMN A/2 /PTO A/2 ) 4 (A is the modulation period) were sucessfully grown. Satellite peaks were observed for these quadrilayer structures and preliminary analysis indicates that for the majority of the tetragonal PTO layers are oriented with the c-axis in the plane of the film.