Preparation, dielectric and ferroelectric properties of Pb5Ge3O11 and Pb5Ge2.85Si0.15O11 thin films fabricated by sol-gel process

Lead germanate-silicate (Pb₅Ge_2.85Si_0.15O₁₁) ferroelectric thin films were successfully fabricated on Pt/Ti/SiO₂/(100)Si substrates by the sol-gel process. The thin films were fabricated by multi-coating at preheating temperatures of 350 and 450 °C. After annealing the thin films at 600 °C, the films exhibited c-axis preferred orientation. The degree of c-axis preferred orientation of the thin films preheated at 350 °C was higher than that of films preheated at 450 °C. Grain growth was influenced by the annealing time. The thin films exhibited a well-saturated ferroelectric P-E hysteresis loop when preheated at 350 °C and annealed at 600 °C for 1.5 h. The values of the remanent polarization (Pr) and the coercive field (Ec) were approximately 2.1 μC/cm² and 100 kV/cm, respectively.     

Structural and magnetic properties of CoFe2O4 thin films deposited by laser ablation on Si (001) substrates

Cobalt ferrite (CoFe₂O₄) thin films have been deposited on Si (001) substrates, with different substrate temperatures (T_dep = 25 °C − 600 °C). The films were prepared by pulsed laser ablation with a KrF excimer laser (wavelength λ = 248 nm). The oxygen pressure during deposition was 2 × 10⁻² mbar. The films structure was studied by X-ray diffraction (XRD) and their surface was examined by scanning electron microscopy (SEM). The magnetic properties were measured with a vibrating sample magnetometer (VSM). For low deposition temperatures, the films presented a mixture of a CoFe₂O₄ phase, with the cubic spinel structure, and cobalt and iron antiferromagnet oxides with CoO and FeO stoichiometries. As the deposition temperature increased, the CoO and FeO relative content strongly decreased, so that for T_dep = 600 °C the films were composed mainly by polycrystalline CoFe₂O₄. The magnetic hysteresis cycles measured in the films were horizontally shifted due to an exchange coupling field (H_exch) originated by the presence of the antiferromagnetic phases. The exchange field decreased with increasing deposition temperature, and was accompanied by a corresponding increase of the coercivity and remanence ratio of the cycles. This behavior was due to the strong reduction of the CoO and FeO content, and to the corresponding dominance of the CoFe₂O₄ phase on the magnetic properties of the thin films.     

Structure, morphology and optical properties of nanocrystalline yttrium oxide (Y2O3) thin films

Yttrium oxide (Y₂O₃) thin films were grown onto Si(1 0 0) substrates using reactive magnetron sputter-deposition at temperatures ranging from room temperature (RT) to 500 °C. The effect of growth temperature (T_s) on the growth behavior, microstructure and optical properties of Y₂O₃ films was investigated. The structural studies employing reflection high-energy electron diffraction RHEED indicate that the films grown at room temperature (RT) are amorphous while the films grown at T_s = 300-500 °C are nanocrystalline and crystallize in cubic structure. Grain-size (L) increases from ∼15 to 40 nm with increasing T_s. Spectroscopic ellipsometry measurements indicate that the size-effects and ultra-microstructure were significant on the optical constants and their dispersion profiles of Y₂O₃ films. A significant enhancement in the index of refraction (n) (from 2.03 to 2.25) is observed in well-defined Y₂O₃ nanocrystalline films compared to that of amorphous Y₂O₃. The observed changes in the optical constants were explained on the basis of increased packing density and crystallinity of the films with increasing T_s. The spectrophotometry analysis indicates the direct nature of the band gap (E_g) in Y₂O₃ films. E_g values vary in the range of 5.91-6.15 eV for Y₂O₃ films grown in the range of RT-500 °C, where the lower E_g values for films grown at lower temperature is attributed to incomplete oxidation and formation of chemical defects. A direct, linear relationship between microstructure and optical parameters found for Y₂O₃ films suggest that tuning optical properties for desired applications can be achieved by controlling the size and structure at the nanoscale dimensions.     

Structure and AC conductivity of nanocrystalline Yttrium oxide thin films

Yttrium oxide (Y₂O₃) thin films were grown at substrate temperatures (T_s) ranging from room temperature (RT) to 500 °C and their structural and electrical properties were evaluated. The results indicate that Y₂O₃ films grown at RT-100 °C were amorphous (a-Y₂O₃). Y₂O₃ films began to show cubic phase (c-Y₂O₃) at T_s = 200 °C. The average grain size varies from 5 to 40 nm as a function of T_s. Room temperature ac electrical conductivity increases from 0.4 (Ω-m)^− 1 to 1.2 (Ω-m)^− 1 with increasing T_s from RT to 500 °C. The frequency dispersion of the electrical resistivity reveals the hopping conduction mechanism. Frequency dispersion of the electrical resistivity fits to the modified Debye's function, which considers more than one ion contributing to the relaxation process. The mean relaxation time decreases from 2.8 to 1.4 μs with increasing T_s indicating that the effect of microstructure of the Y₂O₃ films is significant on the electrical properties.     

Stability and effect of annealing on the optical properties of plasma-deposited Ta2O5 and Nb2O5 films

Tantalum and niobium oxide optical thin films were prepared at room temperature by plasma-enhanced chemical vapor deposition using tantalum and niobium pentaethoxide (M(OC₂H₅)₅) precursors. We studied the evolution of their optical and microstructural properties as a result of annealing over a broad temperature range from room temperature up to 900 °C. The as-deposited films were amorphous; their refractive index, n, and extinction coefficient, k, at 550 nm were n = 2.13 and k < 10^− 4 for Ta₂O₅, and n = 2.24 and k < 10^− 4 for Nb₂O₅. The films contained a small amount of residual carbon (∼ 2-6 at.%) bonded mostly to oxygen. During annealing, the onset of crystallization was observed at approximately T_C1 = 650 °C for Ta₂O₅ and at T_C1 = 450 °C for Nb₂O₅. Upon annealing close to T₁ (300 °C for Nb₂O₅ and 400 °C for Ta₂O₅), n at 550 nm decreased by less than 1%. This was correlated with the decrease of carbon content, as suggested by Fourier transform infrared spectroscopy, elastic recoil detection and static secondary ion mass spectroscopy (SIMS) results. During annealing, we observed phase transition from the δ- (hexagonal) phase to the L- (orthorhombic) phase between 800 °C and 900 °C for Ta₂O₅, and between 600 °C and 700 °C for Nb₂O₅. The structural changes were also marked by silicon diffusion from the substrate into the oxide layer at annealing temperatures above 500 °C for Ta₂O₅ and above 400 °C for Nb₂O₅. As a consequence of oxygen, silicon and metal interdiffusion, the interface between the Si substrate and the metal oxide (Ta₂O₅ or Nb₂O₅) is characterized by its broadening, well documented by spectroscopic ellipsometry and SIMS data.     

Luminescence properties of Ba2LiB5O10:Dy phosphor

A novel warm white phosphor Ba₂LiB₅O₁₀:Dy³⁺ with various Dy³⁺ concentrations was synthesized by the conventional solid-state reaction at 800 °C. The crystal structure of the phosphor was characterized by X-ray diffraction (XRD). The photoluminescence properties of Ba₂LiB₅O₁₀:Dy³⁺ were investigated, and the critical concentration of the activator ion (Dy³⁺) was found to be 0.04 mol per formula unit. Under the ultraviolet excitation of 348 nm, the phosphor presented warm white luminescence with dominating emissions at 484.6 and 577 nm, corresponding to ⁴F_9/2-⁶H_15/2, ⁴F_9/2-⁶H_13/2 transitions, respectively. The chromatic properties of the typical sample Ba₂LiB₅O₁₀:0.04Dy³⁺ phosphor have been found to have chromaticity coordinates of x = 0.31 and y = 0.35.     

Formation of NiFe2O4 nanoparticles by mechanochemical reaction

Preparation of nanosized NiFe₂O₄ particles by mechanochemical reaction(NiO+α-Fe₂O₃) and subsequent thermal treatment was investigated using X-ray diffraction (XRD). Thermal treatment of the as-milled powder at 700 °C for 1 h led to the formation of NiFe₂O₄ nanoparticles with an average crystal size of about 23 nm. Effect of thermal treatment temperature on the crystal size of the nanoparticles was studied. The mechanism of nanoparticles growth was primarily discussed. The activation energy of NiFe₂O₄ nanoparticle formation during calcination was calculated to be 16.6 kJ/mol.     

Processing, dielectric properties and impedance characteristics of Na0.5Bi0.5Cu3Ti4O12 ceramics

Na_0.5Bi_0.5Cu₃Ti₄O₁₂ (NBCTO) ceramics were prepared by conventional solid-state reaction method. The phase structure, microstructure and dielectric properties of NBCTO ceramics sintered at various temperatures with different soaking time were investigated. Pure NBCTO phase could be obtained with increasing the temperature and prolonging the soaking time. High dielectric permittivity (13,495) and low dielectric loss (0.031) could be obtained when the ceramics were sintered at 1000 °C for 7.5 h. The ceramics sintered at 1000 °C for 7.5 h also showed good temperature stability (−4.00 to −0.69%) over a large temperature range from −50 to 150 °C. Complex impedances results revealed that the grain was semiconducting and the grain boundaries was insulating. The grain resistance (R_g) was 12.10 Ω cm and the grain boundary resistance (R_gb) was 2.009 × 10⁵ Ω cm when the ceramics were sintered at 1000 °C for 7.5 h.     

Ferroelectric properties of Bi3.4Dy0.6Ti3O12 thin films crystallized in N2

Bi_3.4Dy_0.6Ti₃O₁₂ (BDT) ferroelectric thin films were deposited on Pt/Ti/SiO2/Si substrates by chemical solution deposition (CSD) and annealed in an N₂ environment after pre-annealing in air at 400 °C. The effect of crystallization temperature on the structural and electrical properties of the BDT films was studied. The BDT films annealed in N₂ in the temperature range of 600 °C to 750 °C were crystallized well and the average grain size increased with increasing crystallization temperature, while the remanent polarization of the films is not a monotonic function of the crystallization temperature. The BDT films crystallized at 650 °C have the largest remanent polarization value of 2P_r = 39.4 μC/cm², and a fatigue-free characteristic.     

Optical and electrical properties of heat-resistant Sb-doped Sn1 − xHfxO2 transparent conducting films

To examine variations in the transparent conducting properties after annealing at high temperatures, 300-nm thick Sb-doped Sn_1 − xHf_xO₂ (x = 0.00-0.10) films were deposited onto silica glass substrates by the RF sputtering method and annealed in air up to 1000 °C at 200 °C increments. After annealing, all the Sb-doped SnO₂ films were transparent and electrically conductive, but large cracks, which decreased the electrical conductivity, were generated in several films due to crystallization or the thermal expansion difference between the film and substrate. Only the film deposited at room temperature in an Ar and O₂ mixed atmosphere did not crack after annealing, and its electrical conductivity exceeded 100 S cm^− 1 even after annealing at 1000 °C in air. Hf-doping blue shifted the fundamental absorption edges in the UV region in the Sb-doped Sn_1 − xHf_xO₂ films. Additionally, the optical transmission at 310 nm, T₃₁₀, increased as the Hf concentration increased, whereas the electrical conductivity was inversely proportional to the Hf concentration. On the other hand, thinner films (150-nm thick) with x = 0.00 showed both a high electrical conductivity over 100 S cm^− 1 and a high transparency T₃₁₀ = 65% after high temperature annealing.     

Effects of Ti on dielectric and piezoelectric properties of (Pb0.985La0.01)1+y(Nb1−yTiy)2O6 ceramics

Piezoelectric ceramics (Pb_0.985La_0.01)_1+y(Nb_1−yTi_y)₂O₆ (0 ? y ? 0.1) (PLNT) were fabricated by a conventional solid-state reaction method. The crystal structure and microstructures of specimens were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). All PLNT ceramics sintered at temperatures from 1250 °C to 1290 °C are shown to be a single orthorhombic phase. The formation of orthorhombic phase is promoted by excess PbO existed in the Ti-bearing samples during calcination processing. The increasing of the tolerance factor due to substitution of Ti⁴⁺ for Nb⁵⁺ is also responsible for the stability of orthorhombic phase. The high density of ceramics (relative density >95%) with the equiaxed grains and a minor porosity have been obtained. The measurement of dielectric and piezoelectric properties of PLNT ceramics reveals that Ti reduces the dielectric loss (tan δ) and dielectric constant (ε_r) of PLNT ceramics, and enhances the piezoelectric constant (d₃₃) and Curie temperature (T_c). The optimum component with y = 0.075 possesses the excellent electrical properties: ε_r = 182, tan δ = 0.0018, d₃₃ = 84 pC/N and T_c = 564 °C.     

Subsolidus phase equilibria and the Li5Nd4FeO10 phase in the Li2O-Nd2O3-Fe2O3 system

A survey of the subsolidus phase equilibria in the system Li₂O-Nd₂O₃-Fe₂O₃ was made at subsolidus temperatures in the range 1000-1050 °C. A ternary phase was identified. The phase is centered on Li₅Nd₄FeO₁₀, with a cubic lattice a = 11.9494 Å. The compound melts incongruently at 1105 °C. The magnetic susceptibility was measured in the temperature range 4-300 K. The compound is paramagnetic in the temperature range 150-300 K and follows the Curie-Weiss law. At about T_N = 10 K, a long-range magnetic ordering is observed.     

Grazing incidence X-ray study of Ge-nanoparticle formation in (Ge:SiO2)/SiO2 multilayers

We present the study of formation of Ge-nanoparticles (Ge-NP) in germanosilicate (Ge:SiO₂) multilayer (ML) films under thermal treatment. In anticipation of controllable formation of Ge-NP, ML films were prepared by magnetron deposition at room temperature as 20 bi-layer stacks, each bi-layer comprised of a 7 nm thick layer of (Ge + SiO₂) (molar ratio: 60:40) succeeded by a 7 nm thick layer of pure SiO₂, and then annealed for 1 h, up to T_a = 900 °C. Formation and morphology of Ge-NP were analyzed by combining the information obtained from the grazing incidence small angle X-ray scattering and X-ray diffraction. It was found that precipitation of Ge-NP starts at T_a = 600 °C, while high degree of in-plane confinement and lateral ordering of rather uniform precipitated particles is achieved at T_a =  700-800 °C range. At still higher annealing temperature T_a > 800 °C, volume fraction of precipitated Ge-NP in SiO₂ matrix diminishes due to the out-diffusion of Ge atoms from the film, while Ge-NP are no more well confined to (Ge + SiO₂) layers.     

ZnFe2O4 thin films from a single source precursor by aerosol assisted chemical vapour deposition

A single source heterobimetallic complex [Fe₂(acac)₄(dmaeH)₂][ZnCl₄] (1) (acac = 2,4-pentanedionate, dmaeH = N,N-dimethylaminoethanol), was synthesized in high yield. The complex was analyzed by melting point, Fourier transfer infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). The structure of the cation was established by single crystal X-ray analysis on a derivative, [Fe₂(acac)₄(dmaeH)₂][ZnCl₃(THF)]₂·THF (1a) (THF = tetrahydrofuran). TGA analysis showed that complex (1) undergoes facile thermal decomposition at 450 °C to give ZnFe₂O₄ residue. In-house designed aerosol assisted chemical vapour deposition equipment was used to deposit thin films of ZnFe₂O₄ on fluorine doped SnO₂ coated conducting glass substrate at 450 °C. X-ray diffraction analysis proved the formation of crystalline ZnFe₂O₄ phase and scanning electron microscopy revealed the film morphology with well defined crystalline particles evenly distributed in the range 150-200 nm. The indirect and direct bandgap energies of the thin films were estimated to be 1.76 and 2.10 eV, respectively.     

Scaling behavior and structure transition of ZrO2 films deposited by RF magnetron sputtering

ZrO₂ thin films were deposited onto Si wafers and glass slides by reactive rf magnetron sputtering with varying conditions of substrate temperature (T_s). Structural analysis was carried out using high-resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM). The scaling behavior of the AFM topographical profiles was analyzed using one-dimensional power spectral density method (1DPSD). Morphological and structural evolution of ZrO₂ films have been studied in relation to T_s. With substrate temperatures ranging from RT to 550 °C, the structural transition of the films is a-ZrO₂ (below 250 °C) → m-ZrO₂ with a little a-ZrO₂ (450 °C) → m-ZrO₂ with a little t-ZrO₂ (550 °C). The roughness exponent α is 1.53 ± 0.02, 1.04 ± 0.01, 1.06 ± 0.05, 1.20 ± 0.03 for ZrO₂ thin films deposited at RT, 250 °C, 450 °C, and 550 °C, respectively. Quantitative surface characterization by spatially resolved 1DPSD analyses identified three different growth mechanisms of surface morphology for ZrO₂ thin films deposited at RT, 250∼450 °C and 550 °C. The evolution and interactions of surface roughness and microstructure are discussed in terms of surface diffusion, grain growth, and flux shadowing mechanisms.     

Physicochemical properties of solid-solid interactions in nanosized NiO-substituted Fe2O3/TiO2 system at 1200 °C

The solid-solid interactions between nanosized pure and NiO-substituted ferric and titanium(IV) oxides have been investigated using XRD technique and microstructure studies, also magnetic properties were studied using vibrating samples magnetometer (VSM). The amounts of substituting Ni²⁺ were x = 0, 0.2, 0.4, 0.6, 0.8 and 1 mole. A mixture equimolar proportions of finely powdered Fe₂O₃ and TiO₂ were mixed with NiO, ball milled, compressed at 250 kg/cm² and fired at 1200 °C for 4 h.The obtained results showed that with substituting Ni²⁺ concentration x = 0 only Fe₂TiO₅ phase is present (∼80 nm) which showed a very small saturation magnetic flux density (B_s), remnant magnetic flux density (B_r) and the maximum energy product (BH)_max. By the addition of x = 0.2 NiO, new phases were observed NiTiO₃ and NiFe₂O₄ of crystallite sizes 160 and 110 nm, respectively. By the increase of substituting Ni²⁺ concentration the NiTiO₃ and NiFe₂O₄ phases increased on the expense of Fe₂TiO₅ up to x = 0.4, then the increase in substituting Ni²⁺ concentration led to a decrease in Fe₂TiO₅ and NiTiO₃ while NiFe₂O₄ increases which results in a great improvement of magnetic properties.All samples exhibit a catalytic activity towards H₂O₂ decomposition and the values of rate constant increase with increasing amount of Ni²⁺ substituting. The most acidic active sites are shown by specimens substituted with x = 0 this concludes that H₂O₂ decomposition is not favored on acidic active sites.     

Properties of La-substituted Na0.5Bi4.5Ti4O15 ferroelectric thin films

Ferroelectric Na_0.5La_0.5Bi₄Ti₄O₁₅ (NaLaBTi) thin films were prepared by a chemical solution deposition method. The NaLaBTi thin films annealed at 750 °C under oxygen atmosphere were randomly oriented polycrystalline. Electrical properties of the NaLaBTi thin films were compared to Na_0.5Bi_4.5Ti₄O₁₅ thin films and better properties were observed in the NaLaBTi thin films. Remnant polarization (2P_r) and coercive electric field (2E_c) were 43 µC/cm² and 204 kV/cm at an applied electric field of 478 kV/cm, respectively. Leakage current density was 1.95 × 10^− 6 A/cm² at 100 kV/cm. Dielectric constant and dielectric loss were 805 and 0.05 at 1 kHz, respectively. Switchable polarization was suppressed by 15% after 1.44 × 10¹⁰ switching cycles.     

The effect of Cu content on the structure of Ni1−xCuxFe2O4 spinels

A series of Ni_1−xCu_xFe₂O₄ (0 ≤ x ≤ 0.5) spinels were synthesized employing sol-gel combustion method at 400 °C. The decomposition process was monitored by thermal analysis, and the synthesized nanocrystallites were characterized by X-ray diffraction, transmission electron microscopy, infra-red and X-ray photoelectron spectroscopy. The decomposition process and ferritization occur simultaneously over the temperature range from 280 °C to 350 °C. TEM indicates the increase of lattice parameter and particle size with the increase of copper content in accordance with the XRD analysis. Cu²⁺ can enter the cubic spinel phase and occupy preferentially the B-sites within x = 0.3, and redundant copper forms CuO phase separately. A broadening of the O 1s region increases with the increment of copper content compared to pure NiFe₂O₄, showing different surface oxygen species from the spinel and CuO. Cu²⁺ substitution favors the occupancy of A-sites by Fe³⁺.     

Effect of annealing on the characteristics of Au layers grown on the high-temperature deposited Ni50Fe50 layers

80 nm-thick Ni₅₀Fe₅₀ layers were sputter-deposited on glass substrates at 400 °C and then Au layers were sputter-deposited on the Ni₅₀Fe₅₀ layers. The Au/Ni₅₀Fe₅₀ bilayer films were annealed in a vacuum of 5×10⁻⁴ Pa from 250 to 450 °C for 30 min or 90 min. The characteristics of the Au layers were studied by Auger electron spectroscopy, field emission scanning electron microscopy, X-ray diffraction and a four-point probe technique. When the annealing temperature reaches 450 °C, Fe and Ni atoms diffuse markedly into the Au layer and the Fe content is more than the Ni content. When the annealing temperature is lower than 450 °C, the grain size of the Au layers does not change markedly with annealing temperature. However, as the annealing temperature reaches 450 °C, the annealing promotes the grain growth of the Au layer. As the annealing temperature exceeds 300 °C, the resistivity of the bilayer films increases with increasing annealing temperature. The diffusion of Fe and Ni atoms into the Au layer results in an increase in the resistivity of the annealed bilayer film. Large numbers of Fe and Ni atoms diffusing into the Au layer of the annealed Au/Ni₅₀Fe₅₀ bilayer film lead to a significant decrease in the lattice constant of the Au layer.     

Properties of screen-printed Ho-Ba-Cu-O films on YSZ substrates

High-T_c screen-printed Ho-Ba-Cu-O films were prepared on YSZ substrates by a melt processing method. The films were fired at T_s = 1000-1050 °C for 5 min and cooled to 450 °C by two steps in flowing O₂. The maximum critical current density J_c (77 K, 0 T) of 2.0 × 10³ A cm^− 2 was only attained under much limited firing conditions; T_s = 1020 °C and cooled to 800 °C at a cooling rate of 400 °C h^− 1.