Relaxation Of Thin Films Research Articles

Effect of high pressure on relaxor ferroelectrics

We report results of a high-pressure investigation by Raman spectroscopy of a classic relaxor ferroelectric (relaxor) ${\mathrm{PbMg}}_{1/3}{\mathrm{Nb}}_{2/3}{\mathrm{O}}_{3}$ (PMN), which is considered to be a model system for the understanding of relaxor and relaxor-related materials. The observed pressure-dependent Raman spectra are very unusual, pointing to a relaxor-specific spectral signature. We further show that an external pressure of several GPa, as can be met in thin films, alters fundamentally the structural and polar properties of PMN, suggesting that intrinsic instabilities towards pressure play an important role in the reduction of dielectric properties in relaxor and relaxor-related thin films.

Effect of thermal expansion mismatch on the dielectric peak temperature of thin film relaxors

Strongly oriented thin film capacitors of Pb(Mg1/3Nb2/3)O3 were made by pulsed laser deposition and found to show a decreased temperature of the dielectric maximum (Tm) relative to bulk. The in-plane strain was measured and found to be compressive, a feature that is normally associated with increased Curie temperatures in conventional ferroelectrics. Other features, such as a more pronounced frequency dependence of Tm in thin films than in bulk, were also noted. An attempt to rationalize these differences by consideration of thermal expansion mismatch between substrate and film is presented. The shifts in Tm are modeled using a semiempirical Landau–Ginzburg–Devonshire model, in which the first coefficient of the thermodynamic potential has been modified to have a quadratic, rather than linear, temperature dependence. The predictions of the model are compared with experimental results from this work and other reports on relaxor thin films extracted from the literature.

Single-crystal, mesoscopic films of lead zinc niobate-lead titanate: Formation and micro-Raman analysis

A process to form thin films of lead zinc niobate–lead titanate (PZN–PT) from a bulk crystal for microelectronic and microelectromechanical device applications is presented. The structural phase transitions and ferroelectric ordering in unpoled crystalline bulk and thin-film relaxor PZN–PT are studied from −190 °C to 600 °C using polarized micro-Raman scattering. The structural phase transitions in this material are observed by distinct changes in the polarization selectivity. The results for the thin film and bulk crystal are in good agreement for a wide range of the temperatures studied, indicating that the thin-film PZN–PT retains much, if not all, of the structural and ferroelectric properties of the original bulk substrate.

Enhancement of dielectric constant and associated coupling of polarization behavior in thin film relaxor superlattices

Thin film capacitor structures in which the dielectric is composed of superlattices of the relaxors [0.2Pb(Zn1/3Nb2/3)O3–0.8BaTiO3] and Pb(Mg1/3Nb2/3)O3 have been fabricated by pulsed laser deposition. Superlattice wavelength (Λ) was varied between ∼3 and ∼600 nm, and dielectric properties were investigated as a function of Λ. Progressive enhancement of the dielectric constant was observed on decreasing Λ, and, in contrast to previous work, this was not associated with the onset of Maxwell–Wagner behavior. Polarization measurements as a function of temperature suggested that the observed enhancement in dielectric constant was associated with the onset of a coupled response. The superlattice wavelength (Λ=20 nm) at which coupled functional behavior became apparent is comparable to that found in literature for the onset of coupled structural behavior (between Λ=5 nm and Λ=10 nm).

Interfacial Mismatch and Interface Structure of Epitaxial Pb(Mg1/3Nb2/3)O3 (90%)- PbTiO3 (10%) Relaxor Thin Films

Abstract Pb(Mg1/3Nb2/3)O3 (PMN)- and its solid solution with PbTiO3 (PT) is one of the lead-based relaxor ferroelectrics and has been the most widely studied materials because of their high dielectric constants and high electrostrictive coefficients. The potential impact of the thin film ferroelectric relaxors in the integrated actuators and sensing applications has stimulated research on the growth and characterization of thin films. Thin films have been made by pulsed-laser deposition (PLD), sol-gel and metalrganic chemical-vapor deposition. It is known that electrical properties may be strongly influenced by the microstructure of films and the interface structures between different phase in such heterostructure systems. In this paper, we report the investigation of interfacial mismatch and interface structure of epitaxial Pb(Mg1/3Nb2/3)O3 (90%)- PbTiO3 (10%) relaxor thin film by high resolution transmission electron microscopy (HRTEM). Thin film capacitors of Pb(Mg1/3Nb2/3)O3 (90%) - PbTiO3 (10%) (PMN-PT) were grown by PLD on (100)-oriented LaA1O3 (LAO) substrates. La0.5Sr0.5CoO3 (LSCO) layer was deposited as electrode. Cross-sectional transmission electron microscopy samples were prepared following the traditional procedures including cutting, gluing, polishing and ion milling.

Role of substrate on the dielectric and piezoelectric behavior of epitaxial lead magnesium niobate-lead titanate relaxor thin films

The effect of various substrates on the electrical and electromechanical properties of 100-nm-thick epitaxial 0.9[Pb(Mg1/3Nb2/3)O3]–0.1[PbTiO3](0.9PMN–0.1PT) thin films is investigated. (001) 0.9PMN–0.1PT films are grown on (001)LaAlO3(LAO), (La, Sr)(Al, Ta)O3(LSAT), SrTiO3(STO), and MgO substrates with 40-nm-thick top and bottom La0.5Sr0.5CoO3 electrodes by pulsed laser deposition. X-ray diffraction results indicate that the films on LAO, LSAT, and STO are stressed biaxially in compression in the film-substrate interface whereas the films on MgO are stressed in tension. A decrease in the temperature of dielectric maximum (Tm) together with an increase in the dielectric constant and the longitudinal piezomodulus is observed with decreasing in-plane epitaxial stresses for LAO, LSAT, and STO substrates. The films on MgO substrates have the highest dielectric constant and piezomodulus with Tm below room temperature. The variation in Tm may be attributed to the shift in the transformation temperature from the paraelectric state to the relaxor state due to internal stresses in the film-substrate interface. Electrical and electromechanical properties should depend strongly on internal stresses in the vicinity of the phase transformation, which is reflected in our experimental observations.

Investigation into the growth and electromechanical properties of Pb(Mg 1/3 Nb 2/3 )O 3 thin films

Pulsed laser deposition (PLD) has been used to fabricate relaxor thin films and thin film capacitors based on the Pb(Mg1/3Nb2/3)O3 system. Best capacitor structures show dielectric constants (ɛr) of ∼1000 and losses (tan δ) ∼0.02 at 1 kHz at 300 K. Electromechanical investigations show that tensile longitudinal strains of up to 0.2% can be achieved in these films.

Effect of mechanical constraint on the dielectric and piezoelectric behavior of epitaxial Pb(Mg1/3Nb2/3)O3(90%)–PbTiO3(10%) relaxor thin films

The effect of heteroepitaxy-induced constraint on the structure and piezoelectric properties of the relaxor ferroelectric lead magnesium niobate–lead titanate (PMN–PT) were investigated. Relaxor PMN–PT epitaxial thin films with oxide electrodes were grown by pulsed-laser deposition on (100) LaAlO3 substrates. We observe a systematic decrease in the phase transition temperature (temperature at which a maximum in dielectric response occurs), from around 250 to around 60 °C as the relaxor thickness is increased from 100 to 400 nm. This is accompanied by an increase in the relative dielectric constant (εr), measured at room temperature and 10 kHz, from 300 to 2000. The piezoelectric coefficient d33 measured using a scanned probe microscope, increase by almost an order of magnitude with increasing film thickness.

Electromechanical properties of PMN-PT thin films prepared by pulsed laser deposition technique

Ferroelectric relaxor thin films of the composition 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 (PMN-PT) were fabricated by pulsed laser deposition technique on Pt/Ti/SiO2/Si(100) substrates using a La0.5Sr0.5CoO3 film as a template layer. The films were polycrystalline with random orientation of the grains. Electromechanical properties of the films were evaluated by a sensitive interferometric technique as a function of the dc and ac electric fields and frequency. Experimental results show that the effective piezoelectric coefficient d33 can be tuned over a wide range of magnitudes by varying dc bias fields. A small hysteresis and a low remanent d33 were observed, which favor the use of PMN-PT films in electric field-controlled micromechanical devices. The maximum d33 ranged from 50 to 100 pm/V, depending on the thickness of the films and frequency. The piezoelectric properties are explained based on the expression for the electrostriction biased by polarization. At low electric field, strain is proportional to the square of electric field, while at higher fields it can be better described as the polarization squared. The asymmetry of the strain response in PMN-PT films is attributed to the polarization offset appearing due to the different electrode materials.

The submillimetre dielectric response of a PLZT 9.5/65/35 relaxor thin film

We report on the first quantitative evaluation of the soft-mode behaviour of the relaxor PLZT 9.5/65/35. The transmission spectra of a PLZT thin film deposited on a sapphire substrate were measured in the region at temperatures from 300 up to 523 K, and in the range at 8 - 300 K. We fitted the spectra using the model of classical oscillators, and calculated the parameters of the observed lattice modes. The results were compared with those for bulk ceramics, and satisfactory agreement was achieved. The soft mode is heavily damped, and below room temperature it shows a strong hardening on cooling. Above room temperature, its eigenfrequency levels off, but the corresponding dielectric loss maximum continues to soften weakly down to at 523 K, where the mode becomes overdamped. The lower-frequency data require an additional relaxation below the measured range. Comparison of all of the available data at room temperature points to strong polydispersive losses in the Hz range, and another dispersion region at lower frequencies. We assign them to fluctuations of the polar nanocluster volume, and to reorientations of the cluster polarization, respectively. Their contribution to the low-frequency permittivity is much stronger than that of the soft mode.

Dielectric and Pyroelectric Characteristics of Plzt (9.5/65/35) Relaxor Thin Films

AbstractFerroelectric relaxor thin films of lead lanthanide zirconate titanate (PLZT) (9.5/ 65/35) have been deposited by the laser ablation technique onto metallized silicon and lanthanum aluminate substrates. The dielectric and pyroelectric properties of PLZT films and their temperature dependencies have been investigated in some detail in an evaluation of their potential as prospective pyroelectric infrared (IR) detector materials. The temperature at which the dielectric constant of a PLZT film reaches its peak is different from that for the peak pyroelectric coefficient. A lower dielectric constant at which the pyroelectric peak appears contributes to a high figure of merit for PLZT films, so that it is competitive with its ceramic counterpart, as well as with Pb(Mg1/3Nb2/3)O3 (PMN) relaxor ferroelectric ceramic.

Tunable Dielectric and Piezoelectric Characteristics of Lead Magnesium Niobate Titanate Relaxor Thin Films

AbstractFerroelectric relaxor thin films Pb[(Mg1/3Nb2/3)0.9Ti0.1]O3 (90PMNIOPT) have been fabricated by the sol-gel technique. The dielectric, piezoelectric and electrostrictive characteristics have been investigated. Experimental results show that the dielectric permittivity and effective piezoelectric coefficients of the films can be tuned by varying dc bias fields which offers the useful features in designing smart micro transducer and actuator systems. Dielectric constants of the films are in the range of 5000 to 6000. The electric field induced strain is on the order of 10−3, and the maximum effective d33 coefficient of 90PMINI0PT films is as large as 265 pC/N at 31 kV/cm. The electrostrictive coefficient Q11 is on the order of 1.2 c×10−2 m4/C2 and M11 is 3.5 c×10−16 m2/V2.