J. Pérez de la Cruz

Thickness effect on the dielectric, ferroelectric, and piezoelectric properties of ferroelectric lead zirconate titanate thin films

Lead zirconate titanate (PbZr0.52Ti0.48O3−PZT) thin films with different thicknesses were deposited on Pt(111)/Ti/SiO2/Si substrates by a sol-gel method. Single perovskite phase with (111)-texture was obtained in the thinnest films, whereas with the increase in thickness the films changed to a highly (100)-oriented state. An increase in the mean grain size as the film thickness increased was also observed. Dielectric, ferroelectric, and piezoelectric properties were analyzed as a function of the film thickness and explained based on film orientation, grain size, domain structure, domain wall motion, and nonswitching interface layers. Both serial and parallel capacitor models were used to analyze the influence of the nonswitching interface layer in the dielectric properties and the effect of substrate clamping in the microscopic piezoelectric response as the film thickness decreased. The scanning force microscopy technique was used to study the effect of thickness on the microscopic piezoresponse. Signific...

Low-temperature dielectric response of NaTaO3 ceramics and films

In this work, NaTaO3 ceramics are prepared by conventional mixed oxide method and NaTaO3 films are deposited by RF magnetron sputtering on Si/SiO2/TiO2/Pt substrates. The dielectric response of the obtained NaTaO3 ceramics and films is analyzed as a function of frequency and temperature. Between 1 kHz and 1 MHz, the dielectric permittivity of NaTaO3 ceramics is frequency independent and increases on cooling up to ∼324, which is the highest value ever reported for NaTaO3 ceramics. In contrast, NaTaO3 films exhibit a dielectric relaxation between ∼20 and 30 K, following the Arrhenius law with activation energy ∼51 meV and pre-exponential term ∼10−15 s and attributed to polaron hopping.

Lithium-induced dielectric relaxations in potassium tantalate ceramics

This work reports the effect of lithium doping on the dielectric and polar properties of potassium tantalate. Experimental data were obtained in K1−xLixTaO3 ceramics with x = 0, 0.02, 0.05 and 0.10 by measuring both the dielectric permittivity from 102 to 108 Hz, and polarization under an ac electric field driven at 2.5 Hz, for temperatures from 10 to 300 K. The dielectric permittivity exhibits all the relaxations reported for K1−xLixTaO3 single crystals. Two dielectric relaxations observed at 40–125 K are ascribed to the individual hopping by 90° and 180° of dipoles created by the off-centre Li ions. Another relaxation observed at 100–200 K is related to 180°-flips of Li pairs for x = 0.02 and of polar clusters of interacting Li ions for x = 0.05 and 0.10. In addition to that, an additional relaxation not reported before is presented at 135–235 K for x = 0.10 and attributed to 90°-reorientation of Li polar clusters. Both the change from an Arrhenius to a Vogel–Fulcher dependence with increasing lithium content, and the emergence of slim P (E) hysteresis loops around the relaxation temperatures show that the relaxation dynamics in K1−xLixTaO3 can be understood if a crossover from a dipolar glass to a relaxor-like behaviour is assumed.

Induced polarized state in intentionally grown oxygen deficient KTaO3 thin films

Deliberately oxygen deficient potassium tantalate thin films were grown by RF magnetron sputtering on Si/SiO2/Ti/Pt substrates. Once they were structurally characterized, the effect of oxygen vacancies on their electric properties was addressed by measuring leakage currents, dielectric constant, electric polarization, and thermally stimulated depolarization currents. By using K2O rich KTaO3 targets and specific deposition conditions, KTaO3−δ oxygen deficient thin films with a K/Ta = 1 ratio were obtained. Room temperature X-ray diffraction patterns show that KTaO3−δ thin films are under a compressive strain of 2.3% relative to KTaO3 crystals. Leakage current results reveal the presence of a conductive mechanism, following the Poole-Frenkel formalism. Furthermore, dielectric, polarization, and depolarization current measurements yield the existence of a polarized state below Tpol ∼ 367 °C. A Cole-Cole dipolar relaxation was also ascertained apparently due to oxygen vacancies induced dipoles. After thermal ...

Persistence of the orthorhombic phase in YMnO3 hexagonal thin films

ABSTRACT YMnO3 thin films were prepared based on a chemical solution deposition route. Their structure was studied as a function of the annealing temperature using X-ray diffraction, Raman spectroscopy, and electron backscatter diffraction. For annealing temperatures above 850°C the films, though crystallizing predominantly in a P63cm hexagonal structure, exhibit a thin Pnma orthorhombic phase close to the film-substrate interface. It is shown that the residual orthorhombic structure is associated with a substrate induced strain state, characterized by an expansion in the in-plane a direction, and a compression in the out of plain c direction.

Unravelling the effect of SrTiO3 antiferrodistortive phase transition on the magnetic properties of La0.7Sr0.3MnO3 thin films

Abstract Epitaxial La 0.7 Sr 0.3 MnO 3 (LSMO) thin films, with different thicknesses ranging from 20 to 330 nm, were deposited on (1 0 0)-oriented strontium titanate (STO) substrates by pulsed laser deposition, with their structure and morphology characterized at room temperature. The magnetic and electric transport properties of the as-processed thin films reveal an abnormal behaviour in the temperature dependent magnetization M ( T ) below the antiferrodistortive STO phase transition ( T STO ), and also an anomaly in the magnetoresistance and electrical resistivity close to the same temperature. Films with thickness ≤100 nm show an in-excess magnetization and pronounced changes in the coercivity due to the interface-mediated magnetoelastic coupling with antiferrodistortive domain wall movement occurring below T STO . However, in thicker LSMO thin films, an in-defect magnetization is observed. This reversed behaviour can be understood with the emergence in the upper layer of the film, of a columnar structure needed to relax the elastic energy stored in the film, which leads to randomly oriented magnetic domain reconstructions. For enough high-applied magnetic fields, as thermodynamic equilibrium is reached, a full suppression of the anomalous magnetization occurs, wherein the temperature dependence of the magnetization starts to follow the expected Brillouin behaviour.Keywords: thin films, magnetic domain reconstruction, interface-mediated coupling, magnetoelasticity(Some figures may appear in colour only in the online journal)

Tackling Polar Response in Oxygen Deficient KTaO3 Thin Films

Oxygen deficient KTaO3 thin films were grown by RF magnetron sputtering on Si/SiO2/Ti/Pt substrates. Room temperature X-ray diffraction shows that they are under a compressive strain of 2.3%. Leakage current results reveal the presence of a conductive mechanism, following Poole-Frenkel formalism. The existence of a polar response below Tpol ∼ 367°C was ascertained by dielectric, polarization, and depolarization current measurements. A Cole-Cole dipolar relaxation was evidenced which is associated with oxygen vacancies induced dipoles. After annealing the films in an oxygen atmosphere above Tpol, the aforementioned polar response is suppressed, due to significant oxygen vacancies reduction.