Effect of annealing time on microstructure and morphology of thin films by sputtering deposition with (Ba<Subscript>0.3</Subscript>Sr<Subscript>0.7</Subscript>)(Zn<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> target

The ceramic thin films have been fabricated by radio frequency (RF) magnetron sputtering technique on SiO₂ (110) substrates with (Ba_0.3Sr_0.7)(Zn_1/3Nb_2/3)O₃ target, and then the thin films were annealed at 1,150 °C for different times at O₂ atmosphere. The microstructure and morphology of the thin films were investigated as a function of the annealing times using the X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy techniques. The results show that the microstructure, morphology, and crystallinity of the thin films can be affected by the annealing times significantly. The main phases of the samples are indexed to be Ba_0.5Sr_0.5Nb₂O₆ and Ba_0.27Sr_0.75Nb₂O_5.78, which are different from component of the (Ba_0.3Sr_0.7)(Zn_1/3Nb_2/3)O₃ target due to the volatilization of ZnO. The crystalline quality of the thin films decreases when the annealing time is shorter or longer than 30 min, and the roughness and grain size of the thin films reaches a maximum value when the annealing time is 30 min.     

Effect of sputtering power on microstructure of dielectric ceramic thin films by RF magnetron sputtering method using (Ba<Subscript>0.3</Subscript>Sr<Subscript>0.7</Subscript>)(Zn<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> as target

Radio frequency (RF) magnetron sputtering method was applied to prepare dielectric ceramic thin films on SiO₂ (110) substrates using (Ba_0.3Sr_0.7)(Zn_1/3Nb_2/3)O₃ microwave dielectric ceramics as target. The samples were deposited at different sputtering powers in Ar atmosphere. In particular, the microstructure and morphology of the thin films were investigated as a function of sputtering powers by X-ray diffraction (XRD), X-ray photoelectron spectroscope (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM). The results show that the thin films are polycrystalline and the sputtering power significantly influences the surface morphology and microstructure of the thin films. On increasing the sputtering power, the crystallinity improves and the grain size and roughness of the thin films reach maximum values at 200 W.     

Influence of annealing times on morphological characteristics of ceramic thin films by RF-magnetron sputtering using Zn-enriched (Ba<Subscript>0.3</Subscript>Sr<Subscript>0.7</Subscript>)(Zn<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> ceramic target

The BaO–SrO–ZnO–Nb₂O₅ ceramic thin films have been deposited by radio frequency (RF) magnetron sputtering, using a Zn-enriched (Ba_0.3Sr_0.7) (Zn_1/3Nb_2/3)O₃ target, followed by annealing in O₂ atmosphere at 1,200 °C for 15, 30, 45, and 60 min. The results show that the surface morphologies of samples are crack-free and compact with well-crystallized structures. Grain sizes of thin films annealed at different times increase with the increasing annealing times, and when the annealing time is of 45 and 60 min, the grains change from spherical shape to columnar shape. RMS values of the thin films decrease with the increase in the annealing times from 15 to 30 min, while the RMS values increase with the increase in the annealing times from 30 to 60 min.     

Optical anisotropy and dielectric parameters of (Ba<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>)Nb<Subscript>2</Subscript>O<Subscript>6</Subscript> films on a Pt(111)/Si(001) substrate

(Ba_0.5Sr_0.5)Nb₂O₆ films were synthesized on a Pt(111)/Si(001) substrate by RF gas-discharge sputtering in pure oxygen atmosphere. It was found that the films have a dominant crystallographic orientation in the [001] direction and natural unipolarity, which was revealed through analysis of dielectric and piezoelectric parameters. It was demonstrated that the optical parameters of film material in the Ba_0.5Sr_0.5, Nb₂O₆/Pt(111)/Si(001) heterostructure match those typical for a (Ba_0.5Sr_0.5)Nb₂O₆ single crystal.     

The Structure,Dielectric, and Optical Properties of <Emphasis Type="Italic">c</Emphasis>-Oriented SBN-50 Films Grown on Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Substrate

Studies of the structure, dielectric and optical properties of thin films of a relaxor ferroelectric Ba_0.5Sr_0.5Nb₂O₆ grown on Pt(111)/Al₂O₃ (c-cut) substrate by high-frequency RF-sputtering in oxygen atmosphere, were performed. X-ray diffraction studies showed that Ba_0.5Sr_0.5Nb₂O₆ films are c-oriented. The unit cell parameters in the tetragonal approximation were c = 3.949(1) Å and a = 12.38(1) Å. It was established that the ferroelectric–paraelectric phase-transition temperature rises and optical anisotropy increases in the object in comparison with the bulk material. Reasons for the elucidated regularities are discussed.     

Effects of oxygen partial pressures on microstructures and compositions of BaO-SrO-ZnO-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> thin films by RF-sputtering method

Ceramic thin films have been deposited by radio frequency magnetron sputtering method, using a mixture of 1 mol (Ba_0.3Sr_0.7)(Zn_1/3Nb_2/3)O₃ and 1 mol ZnO as target. The effects of oxygen partial pressures on crystallization and morphologies of thin films have been investigated in detail by X-ray diffraction, scanning electron microscope (SEM), and atomic force microscope. X-ray photoelectron spectroscopy (XPS) analysis was carried out to identify the composition and chemical state near the films’ surface. It is observed that the diffraction intensity of (001) peak increases dramatically when a small amount of oxygen is added to Ar atmosphere. The cross-sectional SEM images verify that the growth rate decreases sharply due to existence of oxygen, because the thickness decreases from 3.10 μm (pure Ar) to 1.38 μm (O₂/Ar ratio of 0.2:1). The morphologies indicate that the thin films are crackfree with perfect crystallization and all the particles are uniform in size when the O₂/Ar flow ratios are 0.2:1 and 0.4:1. The ceramics thin films grown at O₂/Ar flow ratio of 0.2:1 does not contain adsorbed oxygen, which is confirmed by XPS.     

Effects of annealing temperatures on crystalline quality of ceramic thin films by RF-magnetron sputtering using Zn-enriched (Ba0.3Sr0.7)(Zn1/3Nb2/3)O3 as target

Dielectric ceramic thin film was fabricated on SiO₂ (110) substrates by radio frequency (RF) magnetron sputtering method using a Zn-enriched (Ba_0.3Sr_0.7) (Zn_1/3Nb_2/3)O₃ target followed by annealing in O₂ atmosphere at different temperatures. The effects of annealing temperatures on the crystallization, compositions, microstructures, and morphologies of the ceramic thin films have been investigated in detail. The results showed that all the samples exhibited well- crystallized structures with the main phases of Ba_xSr_1-xNb₂O₆, differing from the target due to volatilization of ZnO. X-ray photoelectron spectroscopy (XPS) analysis shows that only one chemical state is found for each spectrum of Ba, Nb, Sr, Zn and O photoelectron in the films. The surface root-mean-square roughnesses of the thin films decrease with the increasing in the annealing temperatures. Scanning electron microscope (SEM) shows that the surface of the films were crack-free and compact. The spherical grains become large in size with the increase in the annealing temperatures.     

Crystallization and electrical properties of Ba<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>TiO<Subscript>3</Subscript> thin films on SrRuO<Subscript>3</Subscript>/Pt hybrid bottom electrode

Ba_0.7Sr_0.3TiO₃ (BST) thin films were deposited on Pt and SrRuO₃(SRO)/Pt hybrid bottom electrodes by radio frequency magnetron sputtering. X-ray analysis indicated that both films were polycrystalline. Dielectric measurements showed that the films on SRO/Pt hybrid bottom electrode had lower dielectric constant and loss than the films on single Pt and the dielectric properties were frequency-independent. The leakage current density of Ba_0.7Sr_0.3TiO₃ thin films on hybrid bottom electrode was also lower. Leakage mechanism investigations showed that the contact between the electrode-film interfaces of thin films on SRO/Pt hybrid bottom electrode was ohmic. Based on the results, the effects of SRO/Pt hybrid bottom electrode on the crystallization and electrical properties of BST thin films were discussed.     

Electrical behavior of Y-doped Ba<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>TiO<Subscript>3</Subscript> thin films

Ba_0.6Sr_0.4TiO₃ (BST) and 1.5 at% Y-doped Ba_0.6Sr_0.4TiO₃ (Y-BST) thin films have been deposited on single-crystal (100) oriented LaAlO₃ substrates using pulsed-laser deposition technique (PLD), respectively. X-ray diffraction (XRD) scanning revealed that the two kinds of films could be epitaxially grown in pure single-oriented perovskite phases, but Y-BST thin films showed an enhanced crystallization effect. The dielectric properties of the pure and Y-BST thin films were measured at 10 kHz and 300 K with a parallel-plate capacitor configuration. The results revealed that the addition of Y as an acceptor doping is very effective to increase dielectric tunability, and to reduce leakage current of BST thin films. The figure-of-merit (FOM) factor value increases from 17.32 for BST to 25.84 for Y-BST under an applied electric field of 300 kV/cm. The leakage current density of the BST thin films at a negative bias field of 300 kV/cm decreases from 2.45 × 10⁻⁴ A/cm² to 1.55 × 10⁻⁶ A/cm² by Y doping. The obtained results indicated that the Y-doped BST thin film is a promising candidate material for tunable microwave devices.     

Orientation controlling of Pb(Zr<Subscript>0.53</Subscript>Ti<Subscript>0.47</Subscript>)O<Subscript>3</Subscript> thin films prepared on silicon substrates with the thickness of La<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>CoO<Subscript>3</Subscript> electrodes

Pb(Zr_0.53Ti_0.47)O₃ (PZT) thin films were prepared on La_0.5Sr_0.5CoO₃ (LSCO) coated Si substrates by a sol–gel route. The thickness of LSCO electrode was found to modify the preferential orientation of PZT thin films, which consequently affected the dielectric and ferroelectric properties. (100) textured PZT films with dense columnar structure could be obtained on the top of (110) textured LSCO with thickness of 230 nm. PZT thin films prepared on the optimized LSCO films exhibit the enhanced dielectric constant and remnant polarization of 980 and 20 μC/cm², respectively.     

Substrate effect on the properties of La<Subscript>0.775</Subscript>Sr<Subscript>0.225</Subscript>MnO<Subscript>3</Subscript> films

La_0.775Sr_0.225MnO₃ films have been produced by screen printing on various substrates (Al₂O₃, BaTi_0.85Zr_0.11Sn_0.04O₃, Ba_0.996Y_0.004TiO₃, Ba_0.996Y_0.004TiO₃ + 0.04%Mn, and Ba_0.996Y_0.004Ti_0.65Sn_0.35O₃), and their electrical properties have been studied in comparison with those of bulk materials. The structural properties of the substrates are shown to influence the electrical properties of the films.     

Study on dielectric and tunable properties of Cr-doped Ba<Subscript>0</Subscript><Subscript>.6</Subscript>Sr<Subscript>0.4</Subscript>TiO<Subscript>3</Subscript> thin films by rf sputtering

Ba_0.6Sr_0.4TiO₃ dielectric thin films doped by Cr(0, 1, 2.5, 5, 10 mol%) (BSTC) were prepared by radio frequency magnetron sputtering on Pt/Ti/SiO₂/Si substrates. The structure and morphology of the BSTC thin films were studied by atomic force microscopy and X-ray diffraction. The effect of Cr doping on the dielectric properties of BST thin films were analyzed. The results show that the dielectric loss of Cr doping BST thin films is lower than that undoped, and the tunability increased with Cr doping. The thin film doped with 5 mol% Cr has the best dielectric properties. The tunability, loss and figure of merit (FOM) at 1 MHz were 38.9%, 0.0183, and 21.3, respectively.     

The Development of Microstructure and Ferroelectric Properties of Bi<Subscript>4</Subscript>Ti<Subscript>3.96</Subscript>Nb<Subscript>0.04</Subscript>O<Subscript>12</Subscript> Thin Films

Bi₄Ti_3.96Nb_0.04O₁₂ thin films were successfully deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by a sol–gel method and rapid thermal annealing. The effects of Nb-substitution and annealing temperature (500–800°C) on the microstructure and ferroelectric properties of bismuth titanate thin films were investigated. X-ray diffraction analysis reveals that the intensities of (117) peaks are relatively broad and weak at annealing temperatures smaller than 700°C. With the increase of annealing temperature from 500°C to 800°C, the grain size of Bi₄Ti_3.96Nb_0.04O₁₂ thin films increases. The Bi₄Ti_3.96Nb_0.04O₁₂ thin films annealed at 700°C exhibit the highest remanent polarization (2P _r), 36 μC/cm² and lowest coercive field (2E _c), 110 kV/cm. The improved ferroelectric properties can be attributed to the substitution of Nb⁵⁺ to Ti⁴⁺ in Bi₄Ti₃O₁₂ assisting the elimination of defects such as oxygen vacancy and vacancy complexes.     

Effect of nonstoichiometry on the structure and microwave dielectric properties of Ba(Co<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>

Polycrystalline nonstoichiometric Ba(Co_1/3Nb_2/3)O₃ (BCN) materials have been synthesized and investigated. Deviations from stoichiometry have been shown to lead to the formation of crystalline Ba₆CoNb₉O₃₀ (barium deficiency) and Ba₈CoNb₆O₂₄ (cobalt deficiency). The effect of phase composition on the microwave dielectric properties of BCN has been studied. The results demonstrate that the dielectric properties of BCN-based materials can be tuned by varying cobalt content. The materials obtained are high-Q microwave dielectrics with temperature-stable properties.     

Dielectric and piezoelectric properties of MnO<Subscript>2</Subscript>-doped K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>Nb<Subscript>0.92</Subscript>Sb<Subscript>0.08</Subscript>O<Subscript>3</Subscript> lead-free ceramics

Lead-free MnO₂-doped K_0.5Na_0.5Nb_0.92Sb_0.08O₃ ceramics have been fabricated by a conventional ceramic technique and their dielectric and piezoelectric properties have been studied. Our results show that a small amount of MnO₂ (0.5–1.0 mol%) is enough to improve the densification of the ceramics and decrease the sintering temperature of the ceramics. The co-effects of MnO₂ doping and Sb-substitution lead to significant improvements in the ferroelectric and piezoelectric properties. The K_0.5Na_0.5Nb_0.92Sb_0.08O₃ ceramic with 0.5 mol%MnO₂ doping possesses optimum propeties: d ₃₃ = 187 pC/N, k _P = 47.2%, ε _r = 980, tanδ = 2.71% and T _c = 287 °C. Due to high tetragonal-orthorhombic phase transition temperature (T _O-T ~ 150 °C), the K_0.5Na_0.5Nb_0.92Sb_0.08O₃ ceramic with 0.5 mol%MnO₂ doping exhibits a good thermal stability of piezoelectric properties.     

Electrical properties of thin Ba<Subscript>x</Subscript>Sr<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>TiO<Subscript>3</Subscript> films on silicon dioxide substrates

We have studied the electrical properties of thin ferroelectric films of barium strontium titanate (Ba_xSr_1−x TiO₃) obtained on fused quartz (SiO₂) substrates by RF magnetron sputtering. Dependences of the tuning coefficient and dielectric loss tangent on the synthesis temperature and the film thickness are reported. The results are compared to analogous data for films grown on polycrystalline alumina substrates.     

Physical properties of lead-free BaFe<Subscript>1/2</Subscript>Nb<Subscript>1/2</Subscript>O<Subscript>3</Subscript> ceramics obtained from mechanochemically synthesized powders

Modern electronics expect functional materials that are eco-friendly and are obtained with lower energy consumption technological processes. The multiferroic lead-free BaFe_1/2Nb_1/2O₃ (BFN) ceramic powder has been prepared by mechanochemical synthesis from simple oxides at room temperature. The development of the synthesis has been monitored by XRD and SEM investigations, after different milling periods. The obtained powders contain large agglomerates built by crystals with an estimated size about 12–20 nm depending on the period of milling. From this powder, the multiferroic BFN ceramic samples have been prepared by uniaxial pressing and subsequent sintering pressureless method. The morphology of the BFN ceramic samples strongly depends on high-energy milling duration. The properties of the ceramic samples have been investigated by dielectric spectroscopy, in broad temperature and frequency ranges. The high-energy milling of the powders has strongly affected the dielectric permittivity and dielectric loss of the BaFe_1/2Nb_1/2O₃ ceramic samples. The usage of the mechanochemical synthesis to obtain the multiferroic lead-free BFN materials reduces the required thermal treatment and simultaneously improves the parameters of the BFN ceramics.     

Low-temperature synthesis of Sr<Subscript>0.3</Subscript>Ba<Subscript>0.7</Subscript>Nb<Subscript>2</Subscript>O<Subscript>6</Subscript> ultrafine powder and its characteristics

Ultrafine strontium barium niobate (Sr_0.3Ba_0.7Nb₂O₆, SBN30) powders were prepared by urea method starting from a precursor solution constituting of Sr (NO₃)₂, Ba (NO₃)₂, NbF₅, urea and polyvinyl alcohol (PVA) as surfactant. Their structural behavior and morphology were examined by means of X-ray diffractometry (XRD) and Scanning electron microscopy (SEM). The results showed that the SBN30 powders crystallized to a pure tetragonal phase at annealing temperatures as low as 750 °C. The average particle size of SBN powders subjected to 750 °C was of the order of 150–300 nm. With increasing calcination temperature,however, the average particle size of the calcined powders increased. The SBN30 ceramic prepared from urea method can be sintered at temperature as low as 1,225 °C. The transition temperature from the ferroelectric phase to the paraelectric phase and the relative dielectric permittivity of the SBN30 powder were less than the corresponding values of the bulk ceramic. The permittivity and loss tangent (tan δ) at room temperature (1 kHz) was found to be 930 and below 0.025.     

Pulsed Laser Deposition of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> with Scanning Beam: Target to Substrate Composition Transfer and Film Structure

Pulsed laser deposition is often considered a process providing congruent transfer of target composition to the growing film. In fact, many different processes affect compositional preservation, starting from incongruent target ablation, to scattering on the way to the substrate, and to processes of the film formation on the substrate surface. We developed a pulsed laser deposition process trying to minimize the compositional deviations due to the scattering by the ambient gas by applying laser beam scanning across the target surface and substitution of oxygen with argon in the chamber during deposition. Transfer of elemental composition of YBa₂Cu₃O₇ targets with compositions varying from stoichiometric 1/2/3 ratio was tested by deposition of thin films in conditions optimal for high-temperature superconductor formation. Despite all measures, the films still show Ba,Y enrichment due to different efficiencies of scattering on the ambient gas. The Y part in the film followed well the composition of the target, but the Ba enrichment was almost constant for most of the studied target compositions, implying a crucial role of the film growth processes. The YBa₂Cu₃O _x (YBCO) films show a layered structure, with increased density of defects in the topmost layer. We suppose this is due to expelling of the excess Ba into the top layer with formation of a quasi-liquid layer promoting formation of a high-density YBCO film.     

Preparation and phase formation of perovskite Pb(Ni<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> by a reaction-sintering process

Pyrochlore-free Pb(Ni_1/3Nb_2/3)O₃ perovskite ceramics produced by a simple and effective reaction-sintering process were investigated. Without any calcination, the mixture of PbO, Ni(NO₃)₂ and Nb₂O₅ was pressed and sintered directly into PNN ceramics. Density of 98.5% of theoretical value was obtained after sintered at 1230 °C for 2 h in air. 99.3% of theoretical density was obtained after sintered at 1,200 °C for 2 h in PbO compensated atmosphere. PNN ceramic with dielectric constant 1,680 at 25 °C and 1 kHz has been obtained.