NbO3 Thin Films Research Articles

Ferroelectric monoclinic phases in strained K0.70Na0.30NbO3 thin films promoting selective surface acoustic wave propagation

We present a detailed analysis of the ferroelectric domain structure of K0.70Na0.30NbO3 thin films on (110) TbScO3 grown by metal–organic chemical vapor deposition. Upon piezoresponse force microscopy and nanofocus x-ray diffraction measurements we derive a domain model revealing monoclinic MC domains. The complex domain pattern is formed out of four co-existing in-plane orientations of the shearing direction of the monoclinic unit cell resulting in four types of superdomains each being composed of well-ordered stripe domains. Finally, we present surface acoustic wave (SAW) experiments that exhibit extraordinary signal intensities given the low thickness of the tested film. Moreover, the SAW propagation is found to occur selectively along the identified shearing directions.

Surface acoustic waves in strain-engineered K0.7Na0.3NbO3 thin films

Epitaxial K0.7Na0.3NbO3 thin films are grown via metal-organic chemical vapor deposition on (110)-oriented TbScO3. The films are strained due to the substrate–film lattice mismatch and therefore exhibit a strong and anisotropic modification of all its ferroelectric properties. The compressive in-plane strain leads to a reduction of the ferroelectric transition temperature from approximately 700 K for unstrained K0.7Na0.3NbO3 to 324 K and 330 K with maximum permittivities of 10 270 and 13 695 for the main crystallographic directions [001]TSO and [11¯0]TSO, respectively. Moreover, the quite thin films (approx. 30 nm thick) exhibit very large piezoelectric properties. For instance, surface acoustic waves with intensities of up to 4.7 dB are recorded for wave propagation along the [11¯0]TSO direction. The signal is smaller (up to 1.3 dB) along [001]TSO, whilst for the intermediate direction [11¯2]TSO, the signal seems to vanish (<0.1 dB). The results indicate that the choice of material, (K,Na)NbO3, in combination with strain-engineering via epitaxial growth onto lattice-mismatched substrates represents a promising way to optimize ferroelectric materials for piezoelectric thin-film applications.

Strain, temperature, and electric-field effects on the phase transition and piezoelectric responses of K0.5Na0.5NbO3 thin films

A KNbO3-based solid solution system is environmentally friendly with good electromechanical performance. This work established the misfit strain–strain and temperature–strain phase diagrams for K0.5Na0.5NbO3 thin films and calculated the polarization switching, phase transition, and piezoelectric responses of K0.5Na0.5NbO3 thin films under various strains, temperatures, and electric fields. The results show that the piezoelectric coefficient d33 can be enhanced near the phase boundaries. For the ferroelectric phase with a nonzero out-of-plane polarization component, an optimal electric field is identified for maximizing d33, which is desired in applications such as thin-film piezoelectric micro-electromechanical systems, transducers for ultrasound medical imaging, and energy harvesting. The present results are expected to provide guidance for the future experimental study of KxNa1−xNbO3 thin films and the optimization of ferroelectric thin film-based devices.

Exploration of Physical Properties on Pure and Ce Doped Sr0.6Ba0.4Nb2O6 Thin Films

Sr0.6Ba0.4Nb2O6 (SBN 60:40) thin films have been grown on various substrates using Radio Frequency (RF) sputtering technique. Influence of cerium ions as the dopant in (SBN 60:40) matrix on its optical absorption, Raman scattering modes and photoluminescence properties have been explored. The modifications observed in the topographical features of pure and cerium doped films have also been studied through atomic force microscopy (AFM). Current-voltage (I-V) characteristics of both virgin and doped films of (SBN 60:40) proclaim the predominant electronic characteristics in the leakage current. The significant results were discussed in detail.

A Novel Multiple Interface Structure with the Segregation of Dopants in Lead‐Free Ferroelectric (K0.5Na0.5)NbO3 Thin Films

AbstractInterfaces in oxides are found to possess different properties and can be engineered for modifying local structure and properties of nearby area. In this work, it is reported that the interfaces can be formed in Ba/Zr (BZ)‐doped (K,Na)NbO3 (KNN) thin films by cycles of chemical solution deposition using same precursor solution. In the films, a novel and special cross‐sectional structure is observed with periodic distribution of Ba‐rich and Zr‐rich layers. The Ba‐rich and Zr‐rich layers exhibit different strain, lattice parameters, and crystal structure, leading to an obvious effect on the general ferroelectric properties of the KNN‐based thin films. Moreover, the self‐polarization is also observed, which can be understood to originate from the formed built‐in field by layered distribution of Ba and Zr in the KNN‐BZ thin films.

Growth of KNN Thin Films for Non‐Linear Optical Applications

Two‐wave mixing is a remarkable area of research in the field of non‐linear optics, finding various applications in the development of opto‐electronic devices, photorefractive waveguides, real time holography, etc. Non‐linear optical properties of ferroelectric potassium sodium niobate (KNN) thin films have been interrogated using two‐wave mixing phenomenon. Regarding this, a‐axis oriented K0.35Na(1‐0.35)NbO3 thin films were successfully grown on epitaxial matched (100) SrTiO3 substrate using pulsed laser deposition (PLD) technique. The uniformly distributed Au micro‐discs of 200 μm diameter were integrated with KNN/STO thin film to study the plasmonic enhancement in the optical response. Beam amplification has been observed as a result of the two‐wave mixing. This is due to the alignment of ferroelectric domains in KNN films and the excitement of plasmons at the metal–dielectric (Au–KNN) interface.

Structural and piezo-ferroelectric properties of K0.5Na0.5NbO3 thin films grown by pulsed laser deposition and tested as sensors

Abstract We have grown K 0.5 Na 0.5 NbO 3 (KNN) films on Pt/TiO 2 /SiO 2 /Si substrates by using pulsed laser deposition. Thin films with pure KNN crystal phase and homogenous morphology were successfully prepared by optimizing the deposition conditions, mainly the oxygen partial pressure and deposition temperature. For oxygen pressure as low as 8 Pa a tungsten-bronze phase is formed, while for higher values i.e. 16 and 32 Pa, the desired KNN perovskite structure is obtained. To prepare pure KNN thin films, a deposition temperature as low as 675 °C is required, however, increasing the temperature to 725 °C promotes better homogeneity and densification of the films. The piezoelectric and ferroelectric behavior, confirmed by piezoresponse force microscopy, revealed a local piezoelectric coefficient of d 33 = 37 pm/V and a coercive voltage of 3.5 V. Finally, we measured the frequency response of this material prepared as a sensor, using the photoacoustic method. This measurement shows that the resonant frequency of a KNN thin film of 230 nm thickness is centered at 3 MHz.

Laser ablated lead free (Na, K) NbO3 thin films with excess alkali-content

Lead free (Na0.5K0.5) NbO3 (NKN) being hygroscopic in nature is very difficult to be fabricated with enhanced properties in thin films. To maintain stoichiometry 0, 5 and 10% mole excess of Na on A-site were added on NKN bulk targets. The perovskite ABO3 crystal structure incorporating 0, 5 and 10% excess alkali ions were grown on Pt/Ti/SiO2/Si substrate by pulsed laser deposition, using stoichiometric high density ceramic targets. X-ray diffraction peaks and Raman scattering spectra suggest the formation of single phase of the film in monoclinic phase. The dielectric properties and leakage current is improved with increasing amount of Na concentration. The reduction in leakage current with addition of excess Na concentration may be due to increase in grain size decrease in the connection of grain boundaries with grains. The impedance spectra of the film shows single dielectric relaxation which is non-debye type and the relaxation frequency is shifted to higher side at higher frequency.

Microwave dielectric and nonlinear optical studies on radio‐frequency sputtered Dy2O3‐doped KNN thin films

AbstractWe report the effect of oxygen mixing percentage (OMP) on structural, microstructural, dielectric, linear, and nonlinear optical properties of Dy2O3‐doped (K0.5Na0.5)NbO3 thin films. The (K0.5Na0.5)NbO3 + 0.5 wt%Dy2O3 (KNN05D) ferroelectric thin films were deposited on to quartz and Pt/Ti/SiO2/Si substrates by RF magnetron sputtering. An increase in the refractive index from 2.08 to 2.21 and a decrease in the optical bandgap from 4.30 to 4.28 eV indicate the improvement in crystallinity, which is also confirmed from Raman studies. A high relative permittivity (εr=281‐332) and low loss tangent (tanδ=1.2%‐1.9%) were obtained for the films deposited in 100% OMP, measured at microwave frequencies (5‐15 GHz). The leakage current of the films found to be as low as 9.90×10−9 A/cm2 at 150 kV/cm and Poole‐Frenkel emission is the dominant conduction mechanism in the films. The third order nonlinear optical properties of the KNN05D films were investigated using modified single beam z‐scan method. The third order nonlinear susceptibility (ǀχ(3)ǀ) values of KNN05D films increased from 0.69×10−3 esu to 1.40×10−3 esu with an increase in OMP. The larger and positive nonlinear refractive index n2=7.04×10−6 cm2/W, and nonlinear absorption coefficient β=1.70 cm/W were obtained for the 100% OMP film, indicating that KNN05D films are good candidates for the applications in nonlinear photonics and high‐frequency devices.

Atomic Resolution Interfacial Structure of Lead-free Ferroelectric K0.5Na0.5NbO3 Thin films Deposited on SrTiO3

Oxide interface engineering has attracted considerable attention since the discovery of its exotic properties induced by lattice strain, dislocation and composition change at the interface. In this paper, the atomic resolution structure and composition of the interface between the lead-free piezoelectric (K0.5Na0.5)NbO3 (KNN) thin films and single-crystalline SrTiO3 substrate were investigated by means of scanning transmission electron microscopy (STEM) combining with electron energy loss spectroscopy (EELS). A sharp epitaxial interface was observed to be a monolayer composed of Nb and Ti cations with a ratio of 3/1. The First-Principles Calculations indicated the interface monolayer showed different electronic structure and played the vital role in the asymmetric charge distribution of KNN thin films near the interface. We also observed the gradual relaxation process for the relatively large lattice strains near the KNN/STO interface, which remarks a good structure modulation behavior of KNN thin films via strain engineering.

Effects of Mn doping on dielectric and ferroelectric characteristics of lead-free (K, Na, Li)NbO3 thin films grown by chemical solution deposition

High-quality lead-free piezoelectric xMn-doped (K0.48Na0.52)0.985Li0.015NbO3 films (KNLN; x = 0, 0.01, 0.02, 0.03) were successfully deposited onto Pt(111)/Ti/SiO2/Si(100) substrates by sol–gel method. Effects of Mn substitution on the microstructure, dielectric properties, ferroelectric properties, and leakage current of the KNLN films were investigated in detail. Mn-doping can significantly improve the ferroelectric properties and decrease the leakage current of KNLN films. Optimal dielectric properties were obtained in films doped with 2 mol% Mn, whose dielectric constant and dielectric loss at 1 kHz were 875 and 0.030, respectively. In addition, well-saturated ferroelectric P-E hysteresis loop with large remanent polarization (2Pr) and coercive field (Ec) of 22.5 μC/cm2 and 65 kV/cm were obtained in 2 mol% Mn-doped KNLN film at an applied electric field of 200 kV/cm.

Lead-free Mn-doped (K0.5,Na0.5)NbO3 piezoelectric thin films for MEMS-based vibrational energy harvester applications

Lead-free Mn-doped (K0.5, Na0.5)NbO3 (KNN) thin films were fabricated by the chemical solution deposition method. The addition of small concentration of Mn dopant effectively reduced the leakage current density and enhanced the piezoelectric properties of the films. The leakage current density of 0.5 mol. % Mn-doped KNN film showed the lowest value of ∼10-7 A/cm2 at 10 V compared to the films with other doping concentrations and the piezoelectric d33 and e31 coefficients of this film were ∼90 pm/V and −8.5 C/m2, respectively. The maximum power and power density of the lead-free thin film-based vibrational energy harvesting device were 3.62 μW and 1800 μW/cm3 at the resonance frequency of 132 Hz and the acceleration of 1.0 G. The results prove that the 0.5 mol. % Mn-doped KNN film is an attractive candidate transducer layer for the piezoelectric MEMS energy harvesting device applications with a small volume and a long-lasting power source.

A Study on (K, Na) NbO<sub>3</sub> Thin Films with Optimized Layer: Effect on Physical and Electrical Properties

(K, Na)NbO3 (KNN) thin films were prepared by sol-gel technique. Spin coating deposition and rapid thermal annealing (RTP) process were applied to produce the KNN thin films. The films obtained demonstrated that highly crystallographic orientation was produced at five layer deposition with increase (preferred orientation) peak at (1 1 1). The thickness of five layers thin films observed by field emission scanning electron microscopy (FE-SEM) was determined to be ~200nm. However, the inhomogeneous distribution of KNN particles was detected in KNN thin films. The distribution of KNN elements was confirmed by energy-dispersive X-ray (EDX) spectra. Improvement was observed in resistivity (2.71-7.81x106 Ω.cm) and dielectric loss (0.35%-0.21%) following the increasing number of layers.

Citrate complexing sol–gel process of lead-free (K,Na)NbO3 ferroelectric films

The citrate complexing sol–gel process to fabricate lead-free (K,[Formula: see text]Na)NbO3 ferroelectric thin films was studied. Soluble niobium source of niobium–citric acid (Nb–CA) solution was utilized as a raw material to synthesize (K,[Formula: see text]Na)NbO3 thin films, by pyrolyzing at 450–550[Formula: see text]C and annealing at 650[Formula: see text]C. The film pyrolyzed at 450[Formula: see text]C shows poor crystallization with porous morphology, whereas the film pyrolyzed at 550[Formula: see text]C appear to be well-crystallized and denser, and the ferroelectricity was also proved by the [Formula: see text]–[Formula: see text] hysteresis loop measurement.

Nonlinear optical properties of pulsed laser deposited Gd2O3 and Dy2O3 doped K0.5Na0.5NbO3 thin films

Abstract We report the structural and nonlinear optical properties of Gd 2 O 3 and Dy 2 O 3 doped (K 0.5 Na 0.5 )NbO 3 (KNN) lead-free thin films fabricated by pulsed laser deposition technique. The crystal structure of the films was analyzed by using Rietveld method. The higher tetragonality and improved surface morphology was observed for the rare-earth oxide doped films. The change in crystal structure and tetragonality with these dopants was explained in terms of change in the internal vibration modes of NbO 6 octahedra. The nonlinear optical properties of the films were measured by using single beam Z-scan technique with a continuous wave He–Ne laser (λ = 632.8 nm). All the films have shown a large third-order nonlinear susceptibility and observed to be enhanced for rare-earth doped KNN thin films (|χ (3) | = 2.69 × 10 −3 esu). The maximum nonlinear refractive index, n 2 = 2.02 × 10 −5 cm 2 /W, and nonlinear absorption coefficient, β = 3.48 cm/W, were obtained for Gd 2 O 3 , and Dy 2 O 3 doped films respectively. These results indicate that rare-earth doped KNN thin films are potential candidates for nonlinear photonic applications.

Optical and dielectric studies on radio frequency sputtered Gd2O3 doped K0.5Na0.5NbO3 thin films for nonlinear photonic and microwave tunable device applications

Abstract (K 0.5 Na 0.5 )NbO 3 +1 wt%Gd 2 O 3 (KNN1G) ferroelectric thin films have been deposited onto quartz and Pt/Ti/SiO 2 /Si substrates by RF magnetron sputtering. The increase in the refractive index, and decrease in the optical bandgap was observed with the oxygen mixing percentage (OMP), and were in the range of 2.07–2.19, and 4.30–4.20 eV, respectively. The dispersion in the refractive index was analyzed using Wemple-DiDomenico single-oscillator model. The refractive index dispersion parameter for the film deposited under 100% OMP is found to be 6.64 × 10 −14 eV m 2 . The best microwave (5 GHz–15 GHz) dielectric properties were observed for the film deposited under pure oxygen plasma. The film deposited in 100% OMP show the relative low leakage current density 4.06 × 10 −6 A/cm 2 at 153 kV/cm and the leakage current of the KNN1G films followed the space charge limited current behaviour. Nonlinear optical property of KNN1G thin films is measured by using modified single beam Z-scan technique. The large third order optical nonlinearity was obtained for the film deposited under pure oxygen plasma with nonlinear refractive index n 2 = 2.46 × 10 −5 cm 2 /W, nonlinear absorption coefficient β = 5.02 cm/W, real and imaginary parts of nonlinear susceptibility are χ R (3) = 3.07 × 10 −3 esu, and χ I (3) = 3.16 × 10 −3 esu, respectively. The obtained results show that the KNN1G thin films have a great potential for nonlinear photonic applications and high frequency applications.

Physical properties of strontium barium niobate thin films prepared by polymeric chemical method

ABSTRACTRandomly oriented Sr0.75Ba0.25Nb2O6 thin films have been deposited on Pt(111)/Ti/SiO2/Si substrates using a polymeric chemical method to study their physical properties. Refinements of the structure confirm the stoichiometry of the studied films. The relaxor behavior is evidenced by the dielectric measurements and Vögel-Fulcher analysis of the dielectric curves. Lowering the transition temperature (Tm) by about 100 K and asymmetries in the local hysteresis loops well above Tm are discussed in terms of the existence of complex defects in thin films.

Annealing temperature effects on the electrical properties of (K, Na) NbO3 thin film fabricated by a sol-gel process with a citrate precursor solution

ABSTRACTUtilizing the comparatively low cost niobium pentoxide (Nb2O5) as raw material, (K,Na)NbO3(KNN) thin films were deposited onto Ti substrate by a sol–gel non-alkoxide process. The effects of annealing temperature on the phase, morphology, dielectric, and ferroelectric properties of KNN thin films were investigated. KNN thin films without impurities were obtained above 700°C, and the microstructure of all films were dense and uniform. A maximum dielectric constant of 480 was obtained in the film annealed at 700°C, which is comparable to the film prepared from niobium ethoxide.

Monoclinic MA domains in anisotropically strained ferroelectric K0.75Na0.25NbO3 films on (110) TbScO3 grown by MOCVD

A highly regular one-dimensional domain pattern is formed in ferroelectric K0.75Na0.25NbO3 thin films grown on (110) TbScO3 substrates using metal–organic chemical vapour deposition (MOCVD). The domain pattern exhibits a lateral periodicity of about 50 nm and extends over several micrometres. The monoclinic symmetry of the domains is controlled by the elastic anisotropy of K0.75Na0.25NbO3 and the anisotropic lattice strain, which is highly compressive in one in-plane direction and weakly tensile in the corresponding orthogonal direction. Using piezoresponse force microscopy and X-ray diffraction, the monoclinic MA phase is identified, which is associated with both a strong vertical and a lateral electric polarization component. The lateral component of the polarization vector is collinear with the ±[{\overline 1}10]pc shear direction of the pseudocubic unit cell of the film and changes periodically by 180° in adjacent domains. A structural variant of a 90° rotated MA domain pattern, where the monoclinic distortion of the pseudocubic unit cells occurs along ±[110]pc, is also observed. However, this variant appears with significantly lower probability, in agreement with energy considerations based on linear elasticity theory. Thus, the incorporation of highly anisotropic lattice strain provides the opportunity to grow one-dimensional nanostructures with high ferroelectric properties.

Swift Heavy Ion (SHI) Irradiation Effects on Pure and Ce Doped Sr0.6Ba0.4Nb2O6 Thin Films

Swift heavy ion irradiation can produce various defects in a target material. However, these defects not necessarily make the material terrible. There is possibility of modifying the properties to make it attractive and enhancing the materials. 150 MeV Ag12+ ions were irradiated on pure and cerium doped SBN films at various ion fluencies viz. 1 x 1011, 1 x 1012 and 5 x 1012 ions/cm2. The effect upon irradiation on the surface properties were studied using XRD measurements. Radiation induced amorphization of the surface at the higher fluence studies was ascertained both through XRD, PL. The surface defects produced after irradiations have been quantified by the way of measurements like average grain size, surface roughness for each of ion fluence through AFM studies. The trapping of charges after irradiation could be perceived from current density measurements. The results were inter correlated with the tools taken for study.