Structure Of PbTiO3 Research Articles

Domain structures of PbTiO3 and Pb(Zr,Ti)O3 thin films controlled by tensile strain induced by a Sr(Zr,Ti)O3 buffer layer

Thin films of Sr(Zr,Ti)O3 were investigated as buffer layers to induce tensile strain in ferroelectric thin films such as PbTiO3 and Pb(Zr,Ti)O3 to control the domain structure. By tuning the composition of Sr(Zr,Ti)O3, (100)-oriented PbTiO3 and Pb(Zr,Ti)O3 films were obtained, revealing that tensile strain was introduced into the thin films by the lattice of the buffer layer. We propose a methodology for the successive control of tensile stress, which is useful for understanding and controlling the domain structures of ferroelectric films that result in the ferroelectric and piezoelectric properties of ferroelectric thin films.

Dielectric and Thermal Properties of Tetragonal PbTiO3 Nanoparticles/Clusters Embedded in Lithium Tetraborate Glass Matrix

PbTiO3 nanoparticles/clusters embedded in lithium tetraborate glass matrix (glass nanocomposite (GNCs)) of composition (100-x) Li2B4O7-xPbTiO3 (where x = 5, 10, 15 and 20 in mol %) were synthesized. The presence of glassy phase in all GNCs samples was identified by X-ray diffraction (XRD) and differential scanning calorimetric (DSC) studies. The structure of PbTiO3 used in the preparation of these samples is a ferroelectric tetragonal phase (space group P4mm) which is confirmed by Rietveld refinement of XRD data. Transmission electron microscopic (TEM) images exhibit PbTiO3 nanoparticles/clusters phase embedded in lithium tetraborate glass matrix. The ferroelectric to paraelectric phase transition of PbTiO3 nanoparticles/clusters in the GNCs samples was established from DSC and dielectric studies. The thermal, density, dielectric and Ac conductivity behavior of the GNCs samples depends on the change in the coordination number of the network former and the concentration of PbTiO3 in the glass matrix.

Elastic Properties and Debye Temperature of Zn Doped PbTiO3 from First Principles Calculation

Zn-doped PbTiO3 has been developed to derive mechanical properties and phase transition. In this paper, a Zn atom 0–16% wt which occupied PbTiO3 structure was investigated by using first principles density functional theory. The generalized gradient approximation was employed to determine the exchange correlation potential. The findings revealed that Zn-doped PbTiO3, calculated through Mulliken population analysis, had atomic (both ionic and covalent) bonding. In addition, the elastic constant satisfied the traditional mechanical stability conditions. Bulk modulus, Young's Modulus and Poisson's Ratio were found to increase with increasing Zn contents. Moreover, the result from the calculated longitudinal sound velocity and transverse sound velocity indicated that Debye temperature for Zn-doped PbTiO3 had more than PbTiO3. Although the Zn-doped PbTiO3 has no reported data for comparisons, it is predicted that Zn-doped PbTiO3 can improve mechanical and dynamics behavior.

Large positive spin polarization and giant inverse tunneling magnetoresistance in Fe/PbTiO3/Fe multiferroic tunnel junction

We perform first-principles electronic structure and spin-dependent transport calculations of a multiferroic tunnel junction (MFTJ) with an epitaxial Fe/PbTiO3/Fe heterostructure. We predict a large positive spin-polarization (SP) and an intriguing giant inverse tunneling magnetoresistance (TMR) ratio in this tunnel junction. We demonstrate that the tunneling properties are determined by ferroelectric (FE) polarization screening and electronic reconstruction at the interface with lower electrostatic potential. The intricate complex band structure of PbTiO3, in particular the lowest decay rates concerning Pb 6pz and Ti 3dz2 states near the Γ¯ point, gives rise to the large positive SP of the tunneling current in the parallel magnetic configuration. However, the giant inverse TMR ratio is attributed to the minority-spin electrons of the interfacial Ti 3dxz+3dyz orbitals which have considerably weight in the extended area around the Γ¯ point at the Fermi energy and causes remarkable contributions to the conductance in the antiparallel magnetic configuration.

Mathematical aspects of Rietveld refinement and crystal structure studies on PbTiO3 ceramics

The core mathematics, goodness-of-fit parameters of Rietveld refinement technique is introduced for structural analysis of crystalline materials not available as single crystals. X-ray diffraction (XRD) patterns of PbTiO3 compound prepared by following solid-state route, suggests it to be in single crystal form. All the observed peaks could be indexed to P4mm space group with tetragonal symmetry. XRD pattern is analysed by employing Rietveld method. The unit cell parameters are found to be a = b = 38987 (0.0008) Å and c = 4·1380 (0·0009) Å. The axial ratio c/a and unit cell volume are found to be 1·0614 and 62·896 (0.023) Å3. Bond lengths and angles are calculated using the cell parameters. Using the Rietveld refinement parameters a stable PbTiO3 structure is suggested.

High-pressure effect on the ferroelectric-paraelectric transition in PbTiO3

The crystal structure of lead titanate PbTiO3 was investigated by energy dispersive X-ray diffraction at high pressures up to 4 GPa in a temperature range of 300–950 K. At the ambient conditions, the PbTiO3 structure is tetragonal with the space group P4mm (ferroelectric phase). A structural phase transition into the cubic phase with a space group $$Pm\bar 3m$$ is observed at T = 747 K. It was found that the phase transition temperature decreases upon applying the high pressure with the coefficient dT C /dP = -65 K/GPa. Dependences of parameters and volume of the unit cell on the pressure and temperature was found, and the bulk modulus and thermal expansion coefficients for the tetragonal and cubic phases of lead titanate have been calculated.

TEM Observation on Ferroelectric Domain Structures of PbTiO<sub>3</sub> Epitaxial Films

The ferroelectric domain structure of PbTiO3(PTO) films was investigated by using transmission electron microscopy (TEM). In the film with PTO/SrTiO3(STO) structure, 180º domains are formed near the SrTiO3(STO) substrate and the domain length of 180º domains is 100 nm. However, 180º domains are not formed in the film with Pt/PTO/SrRuO3(SRO)/STO structure. These results show that 180º domains are formed in order to minimize depolarizing field energy, and that the domain length of 180º domains is determined by the competition among the depolarizing field energy, domain wall energy, Coulomb interaction and elastic interaction.

Local atomic structure of niobates and titanates from X-ray absorption spectroscopic data

The local atomic structure of PbTiO3, BaTiO3, and KNbO3 perovskite-type crystals and K x Na1 − x NbO3 solid solutions in different phases is investigated using the angular dependence of the pre-edge structure of the Ti and Nb K X-ray absorption spectra and the EXAFS data. In noncubic phases, a considerable deviation of the local structure from the structure determined from diffraction data is observed only for the tetragonal phase of the BaTiO3 crystal. It is revealed that, in the cubic phase of niobates, the niobium atoms are characterized by significant displacements from the centrosymmetric positions along the threefold axes, so that they are close in the magnitude and the direction to the displacements in the low-temperatures rhombohedral phases.

Phase transitions in PbTixHf1-xO3 determined by thermal analysis and impedance spectroscopy

The objective of this study is to determine the influence of partial substitutions of Ti4+ by isovalent Hf4+ in the perovskite-type crystalline structure of PbTiO3. Different samples over the whole composition range (0 ≤ x≤1) in the PbTi1-xHfxO3 family have been prepared. Phase transitions have been determined by thermal analysis (differential scanning calorimeter: DSC) and complex impedance spectroscopy (IS) over a wide temperature range. As a consequence of the cation replacement the changes that take place in the different phase transition temperature are reported. By both techniques, thermal analysis and electrical characterization, it is shown that for all compositions prepared there is only one phase transition in a temperature range between 230 and 460 °C. With these results and the previously known crystalline structure of pure PbTiO3 and PbHfO3 perovskites, the phase diagram of the PbTi1-xHfxO3 family is presented including a morphotropic phase transition at x ~ 0.5.

High spontaneous polarization in PbTiO3–BiMeO3 systems with enhanced tetragonality

Pb Ti O 3 – Bi Me O 3 (Me=Fe, Zn1/2Ti1/2, and Zn3/4W1/4) solid solutions exhibit unusually enhanced tetragonality (c/a). Lattice dynamics and structure of PbTiO3–BiMeO3 with enhanced c/a were investigated by Raman scattering technique and x-ray Rietveld method, respectively. The A1(1TO) soft mode, associated with the order parameter spontaneous polarization (PS), abnormally shifts upward, which is different with almost all other PbTiO3-based compounds. It is interesting to find that the A1(1TO) mode increases linearly with the PS displacement. The PS could be basically judged from the variation of A1(1TO) not only with normally reduced c/a but also with unusually enhanced c/a in the PbTiO3-based systems.

Comparative analysis of the atomic structure of crystalline and amorphous PbTiO3 on the basis of the molecular-dynamics simulation data

Models of the atomic structure of PbTiO3 in the crystalline and amorphous states have been constructed by the molecular-dynamics method. The distances between positively charged Pb and Ti ions, which are significantly different in PbTiO3 crystals, are averaged in the amorphous material, forming a common peak in the radial distribution function.

Strain-mediated electric-field control of resistance in the La0.85Sr0.15MnO3∕0.7Pb(Mg1∕3Nb2∕3)O3–0.3PbTiO3 structure

The authors have deposited thin films of La0.85Sr0.15MnO3 (LSMO) on 0.7Pb(Mg1∕3Nb2∕3)O3–0.3PbTiO3 (PMN-PT) single-crystal substrates and have achieved modulation of the resistance of the LSMO film by applying an electric field across the PMN-PT substrate whether the LSMO film is in the paramagnetic, ferromagnetic, or charge-ordered state. Piezoelectric measurements show that the electric field gives rise to a lattice strain in the PMN-PT substrate via the converse piezoelectric effect, which then induces a lattice strain and hence a resistance change in the LSMO film. Analysis of the data indicates that the electric-field-induced lattice strain effect dominates over the field effect in the LSMO/PMN-PT structure.

Effect of synthesis conditions on the structure of PbTiO3

The phase composition of PbTiO3 samples prepared from PbO + TiO2 and PbO + TiO2 · H2O mixtures is determined. The effect of mechanical stress on the structure of PbTiO3 prepared by high-temperature firing of a PbO + TiO2 mixture is investigated experimentally. It is shown that low-temperature synthesis yields not only the perovskite phase of PbTiO3 but also an oxygen-deficient pyrochlore phase with an increased lattice parameter. With increasing temperature, the content of the latter phase drops to zero. The pyrochlore-perovskite phase transition in PbTiO3 is discussed in terms of crystal chemistry and close packing of atoms.

Domain imaging and local piezoelectric response of sol-gel PbTiO3 thin films using SPM

Ferroelectric PbTiO3 thin films have been prepared by sol-gel route, and characterized using scanning probe microscopy. The ferroelectric domain images are obtained in the piezo- response, phase and amplitude measurements respectively, and the resultant contrast is interpreted by the induced local domain piezo-vibration. In particular, 90° and 180° domain walls appear as a transition region and a dark region in the amplitude image with a thickness of 70 nm and 8 nm, respectively. In our randomly oriented PbTiO3 films, the local hysteresis loop measurements exhibit a variety of piezoelectric behaviors, and the additional non-switchable polarization is believed to originate from the asymmetric PbTiO3/Pt heterostructure. Moreover, PbTiO3 film shows an excellent polarization retention performance at the nanometer scale, which may be related to the high tetragonality of PbTiO3 structure.

Ferroelectric domain structures of PbTiO3 studied by scanning force microscopy

The ferroelectric domain morphology ofPbTiO3 single crystals has been investigated at room temperature by electrostatic force microscopy (EFM) and piezoelectric force microscopy (PFM) in addition to atomic force microscopy (AFM). While EFM is shown to reveal 90° a-c-domains via susceptibility contrast and 180° c-domain walls via their stray fields, PFM is used to visualize and to write 180° c-domain patterns. Owing to stabilizing negative space charges provided by the n-type PbTiO3 only negative written c-domains are stable against backswitching.

Ferroelectric domain structure studies on PbTio3 single crystals by polarizing microscope, SEM and AFM

Domain morphologies in pure PbTiO3 single crystals have been investigated. Regular bright and dark stripes on the (001) surface in PbTiO3 have been observed by optical microscope. Direct observation of the domian structure of PbTiO3 is made by using the SEM with an incidence angle of 45°. The 90° domains have been observed with atomic force microscopy (AFM).

Electronic Structures of PbTiO3: I. Covalent Interaction between Ti and O Ions

We calculated the electronic structures of ferroelectric PbTiO3 using the discrete variational Xα cluster method. From our investigation of the π bond between the titanium ion and the oxygen ion, we found that the role of lead ions is to bring about a spatial change in the oxygen 2p orbital by covalent interaction between oxygen 2p and lead 6s orbitals. This change favours titanium ion displacement. Moreover, from the investigation of the σ bond, we found that the role of the Madelung potential is to cause the spatial changes in the titanium orbitals; the long-range Coulomb interaction causes a stronger σ bond. We conclude that the origins of ferroelectricity in PbTiO3 are (i) the spatial change in the oxygen 2p orbital due to covalent interaction between oxygen 2p and lead 6s orbitals and (ii) the spatial changes in the titanium orbitals due to the Madelung potential.

Summary data on ferroelectric PbTiO3 structure

The original data and the data available in literature on PbTiO3 structure are considered and discussed. From the results of an X-ray diffraction study carried out at room temperature it is concluded that the displacive model is more relevant than the order-disorder one. At the same time it is stressed that the Debye-Waller factors of the atoms are very unusual in the region of the phase transition: B(Pb) > B(O) > B(Ti). This may be evidence of order—disorder phenomena taking place in this temperature region.

The effect of stoichiometry on the microstructure and properties of lead lanthanum titanate thin films

Thin films of Lead Lanthanum Titanate (PLT) corresponding to 28 at. % of La were prepared by the metal-organic decomposition (MOD) process. The films were fabricated from two solutions of different composition. The composition of the first solution was determined, assuming that the incorporation of La3+ in the PbTiO3 structure gives rise to A-site or Pb vacancies, whereas for the composition of the other solution the creation of B-site or Ti vacancies was assumed. The effect of excess lead on the microstructure and the optical and electrical properties was studied for 0% to 20% excess PbO. The x-ray diffraction patterns of all films at room temperature indicated a cubic structure with a lattice constant of 3.92 Å. Optical and electrical measurements showed the films made assuming B-site vacancies had better properties. In general, excess PbO was found to improve the optical transmittance as well as the electrical properties of films. However, in films assuming the formation of B-site vacancies, PLT showed improved electrical properties only up to 5–10% excess PbO, while higher PbO additions had a deleterious effect. The films had a high resistivity, good relative permittivity, low loss, very low leakage current density, and high charge storage density. A type-B film with 10% excess Pb had a relative permittivity of 1340 at 100 kHz and a charge storage density of around 16.1 μC/cm2 at a field of 200 kV/cm at room temperature.

Crystalline Structure of PbTiO3 Thin Films by Multiple Cathode Sputtering

The preparation of PbTiO3 thin films by multiple cathode rf-magnetron sputtering was investigated. The effects of incident Pb/Ti ratio, the kind of substrates, substrate temperatures and film thickness on the crystalline structure of the PbTiO3 thin films prepared were studied. The thin films with perovskite PbTiO3 structure on Si wafers were obtained by deposition at an incident Pb/Ti ratio of 1.2 at a substrate temperature of 460∼500°C. The X-ray photoemission spectroscopy (XPS) depth profile revealed that less reaction of the thin films with the Si substrate was observed at the interface at lower substrate temperatures.