Enhanced dielectric properties of Mn doped Ba0.6Sr0.4TiO3 thin films fabricated by pulsed laser deposition

Pure and 2 mol% Mn doped Ba_0.6Sr_0.4TiO₃ (BST) thin films have been deposited on La_0.67Sr_0.33MnO₃ (LSMO) coated single-crystal (001) oriented LaAlO₃ substrates using pulsed-laser deposition technique. The bilayer films of BST and LSMO were epitaxially grown in pure single-oriented perovskite phases for both samples, and an enhanced crystallization effect in the BST film was obtained by the addition of Mn, which were confirmed by X-ray diffraction (XRD) and in situ reflective high energy electron diffraction (RHEED) analyses. The dielectric properties of the BST thin films were measured at 100 kHz and 300 K with a parallel-plate capacitor configuration. The results have revealed that an appropriate concentration acceptor doping is very effective to increase dielectric tunability, and to reduce loss tangent and leakage current of BST thin films. The figure-of-merit (FOM) factor value increases from 11 (undoped) to 40 (Mn doped) under an applied electric field of 200 kV/cm. The leakage current density of the BST thin films at a negative bias field of 200 kV/cm decreases from 2.5 × 10^− 4 A/cm² to 1.1 × 10^− 6 A/cm² by Mn doping. Furthermore, a scanning-tip microwave near-field microscope has been employed to study the local microwave dielectric properties of the BST thin films at 2.48 GHz. The Mn doped BST film is more homogeneous, demonstrating its more potential applications in tunable microwave devices.     

New dielectric materials of xSrTiO3–(1 − x)Ca(Mg1/3Nb2/3)O3 ceramic system at microwave frequency

The crystal structures and the microwave dielectric properties of the xSrTiO₃–(1 − x)Ca(Mg_1/3Nb_2/3)O₃ perovskite ceramic system have been investigated. In order to achieve a temperature-stable material, we studied a method of combining a positive temperature coefficient material with a negative one. SrTiO₃ has dielectric properties of dielectric constant ε_r ∼ 205, Q × f value ∼ 4200 GHz and a large positive τ_f value ∼ 1700 ppm/°C. Ca(Mg_1/3Nb_2/3)O₃ possesses high dielectric constant (ε_r ∼ 28), high quality factor (Q × f value ∼ 58,000 at 7 GHz) and negative τ_f value (− 48 ppm/°C). As the x value varies from 0.2 to 0.8, the xSrTiO₃–(1 − x)Ca(Mg_1/3Nb_2/3)O₃ system has the dielectric properties as follows: 40 < ε_r < 123, 4600 < Q × f < 33,400 and − 23 < τ_f < 600. A new microwave dielectric material, 0.3SrTiO₃–0.7Ca(Mg_1/3Nb_2/3)O₃, applicable in microwave devices is suggested and possesses the dielectric properties of a dielectric constant ε_r ∼ 46, a Q × f value ∼ 29,300 GHz (at 6.8 GHz) and a τ_f value ∼− 2 ppm/°C. A near-zero τ_f value can be achieved by adjusting the x value of xSrTiO₃–(1 − x)Ca(Mg_1/3Nb_2/3)O₃ ceramics.     

Fatigue and retention properties of Bi3.25La0.75Ti3O12 films using LaNiO3 bottom electrodes

Fatigue-free Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films were grown on LaNiO₃ bottom electrodes grown in a microwave furnace at 700 °C for 10 min from the polymeric precursor method. It was found that LaNiO₃ (LNO) bottom electrode with pseudocubic structure strongly promote the formation of (00l) texture of BLT films. The remanent polarization (P_r) and the drive voltage (V_c) were 11 μC/cm² and 1.3 V respectively, and are better than the values found in the literature. The polarization of the Au/BLT/LNO/SiO₂/Si (100) capacitors with a thickness of 280 nm exhibited no degradation after 1 × 10¹⁰ switching cycles at an applied voltage of 5 V with a frequency of 1 MHz. After several tests the capacitors retain 77% of its polarization upon a retention time of 10⁴ s.     

Substrate effect on in-plane dielectric and microwave properties of Ba(Sn0.15Ti0.85)O3 thin films

The microstructure and in-plane dielectric and microwave properties of Barium tin titanate Ba(Sn_0.15Ti_0.85)O₃ (BTS) thin films grown on (1 0 0) LaAlO₃ and (1 0 0) MgO single-crystal substrates through sol–gel process were investigated. X-ray diffraction and field emission scanning electron microscopy were used to characterize crystal structure of phases and microstructure of the thin films, respectively. Microwave properties of the films were measured from 1 to 10 GHz by the interdigital capacitor configuration. The obvious differences in the dielectric and microwave properties are attributed to the stress in the films, which result from the lattice mismatch and difference in the thermal expansion coefficients between the film and substrates. This work clearly reveals the highly promising potential of BTS films for application in tunable microwave devices.     

Efficient laser operation at 1.06 μm in co-doped Lu3+, Nd3+:GdCa4O(BO3)3 single crystal

Efficient laser emission at 1.06 μm was obtained from a diode-laser quasi-continuous wave pumped Nd_0.04Gd_0.86Lu_0.10Ca₄O(BO₃)₃ (Nd:GdLuCOB) single crystal. An uncoated, 6.0-mm long, ZX-cut Nd:GdLuCOB medium yielded laser pulses with 1.76 W peak power for absorbed pump pulses of 5.49 W peak power, corresponding to an overall optical-to-optical efficiency η_oa = 0.32; the slope efficiency was η_sa = 0.44. Comparison is made with an uncoated XY-cut Nd:GdCOB medium (4.0-at.% Nd doping and 6.8-mm length) from which laser pulses with 1.74 W peak power (at optical efficiency η_oa = 0.25) and 0.31 slope efficiency were obtained. The improvements in laser emission of Nd:GdLuCOB at the fundamental wavelength are important for future self-frequency doubling in ZX principal plane of this crystal.     

Fabrication and luminescent properties of Ce:LaAlO3 translucent ceramics

Ce³⁺ doped LaAlO₃ translucent ceramics were fabricated with solid-state reaction method and sintered in vacuum condition. LaAlO₃ single phase was formed at 1200 °C. Their microstructures were observed and luminescent properties were investigated. The average grain size increases with the increase of sintering temperature. A dense and pore-free microstructure is displayed at 1700 °C. A band to band absorption of LaAlO₃ host is round 220 nm. Three excitation peaks at 249, 317 and 354 nm were observed in the Ce³⁺:LaAlO₃ ceramics, they were attributed to the 4f–5d transition of Ce³⁺ ions. The scintillation properties were investigated by X-ray excited radioluminescence in Ce³⁺:LaAlO₃ ceramics and the emission peak is 428 nm.     

Synthesis and characteristics of nature-superlattice-structured Bi3TiNbO9–Bi4Ti3O12 ferroelectric thin films by MOD

Natural-superlattice-structured ferroelectric thin films, Bi₃TiNbO₉–Bi₄Ti₃O₁₂ (BTN–BIT), have been synthesized on Pt/Ti/SiO₂/Si by metal organic decomposition (MOD) using BTN–BIT (1 mol:1 mol) solution. BTN–BIT films show natural-superlattice peaks below 2θ = 20° in X-ray diffraction patterns, which indicate that the BTN–BIT films annealed at 700–800 °C in O₂ ambient are consisted of iteration of two unit cells of Bi₃TiNbO₉ and one unit cell of Bi₄Ti₃O₁₂. As the annealing temperature increases from 600 to 750 °C, uniform and crack-free films, better crystallinity and ferroelectric properties can be obtained, but the pyrochlore phase in BTN–BIT films annealed over 800 °C would impair the ferroelectric properties. With the increase of O₂ flow rate from 0.5 to 1.5 L/min, both remanent polarization P_r and coercive electric field E_C increase, which are mainly attributed to reduction of the vacanvies of Bi and oxide ions in the films. Natural-superlattice-structured BTN–BIT thin films having 2–1 superlattice annealed at 750 °C in O₂ ambient with a flow rate of 1.5 L/min exhibit superior ferroelectric properties of P_r = 23.5 μC/cm² and E_C = 135 kV/cm.     

Microwave dielectric ceramics in (Ca1− xBax)(Zn1 / 3Nb2 / 3)O3 system

(Ca_1−xBa_x)(Zn_1 / 3Nb_2 / 3)O₃ (x = 0–1.0) microwave dielectric ceramics were prepared and investigated. The Ba(Zn_1 / 3Nb_2 / 3)O₃-based solid solution was observed for x = 0.9, and the compositions with x = 0.1–0.7 resulted in the mixture of two phases. Dielectric constant ε_r and temperature coefficient of resonant frequency τ_f of the present ceramics varied anomalously and reached their maximum at x = 0.7–0.9, and these phenomena were originated from the partial substitution of small Ca²⁺ ions for larger Ba²⁺ at A-site. On the other hand, a good combination of microwave dielectric properties (ε_r = 36, Qf = 16,170 GHz, τ_f = − 12 ppm/°C) were obtained at x = 0.1, while the decreased Qf value was observed in other compositions.     

Effect of B2O3 and CuO additives on the sintering temperature and microwave dielectric properties of Ba(Mg1/3Nb2/3)O3 ceramics

B₂O₃ added Ba(Mg_1/3Nb_2/3)O₃ (BBMN) ceramics cannot be sintered below 930 °C. However, when CuO was added to them, they were sintered even at 850 °C. The amount of the Ba₂B₂O₅ second phase, which was formed in the BBMN ceramics decreased with the addition of CuO. Therefore, the CuO additive is considered to react with the B₂O₃ inhibiting the reaction between B₂O₃ and BaO. A dense microstructure without pores developed with the addition of a small amount of CuO. The bulk density, dielectric constant (ɛ_r) and Q-value increased with the addition of CuO, but decreased when a large amount of CuO was added. Excellent microwave dielectric properties were obtained for the Ba(Mg_1/3Nb_2/3)O₃ + 2.0 mol% B₂O₃ + 10.0 mol% CuO ceramic sintered at 875 °C for 2 h, with values Q_xf = 21 500 GHz, ɛ_r = 31 and temperature coefficient of resonance frequency (τ_f) = 21.3 ppm/°C.     

Microwave dielectric properties of novel lithium containing pyrochlore type oxides: Li3Sm3 − xBixTi7Nb2O25 (x = 0, 1, 2 or 3)

Microwave dielectric properties of novel lithium ion containing pyrochlore type oxides: Li₃Sm_3 − xBi_xTi₇Nb₂O₂₅ (x = 0, 1, 2 or 3) have been reported in this paper. Powder X-ray diffraction patterns show that these oxides have cubic pyrochlore type structure. Ceramic microstructure of the sintered samples show well formed grains. They have relatively high dielectric constant (ε_r) in the range 80–137 at 1 MHz and ε_r, 45–83 at the resonant microwave frequency region. It is seen that the dielectric constant (ε_r) increases with the increase of Bi content. The best microwave dielectric properties obtained for fully substituted samarium compound, Li₃Sm₃Ti₇Nb₂O₂₅ are as follows: Q × f = 2007 and ε_r = 45 at the resonant microwave frequency, 3.78 GHz.     

Microwave dielectric properties of Ba(Mg1/3Ta(2−2x)/3Wx/3Tix/3)O3 ceramics

The microwave dielectric properties of ceramics based on Ba(Mg_1/3Ta_(2−2x)/3W_x/3Ti_x/3)O₃ is investigated as a function of x. The densification as well as dielectric properties deteriorate with increase in the substitution levels of (Ti_1/3W_1/3)^3.33+ at (Ta_2/3)^3.33+ site in Ba(Mg_1/3Ta_2/3)O₃. The τ_f is approaching zero between x = 0.1 and 0.15 in Ba(Mg_1/3Ta_(2−2x)/3W_x/3Ti_x/3)O₃ where quality factor is reasonably good (Q_u × f = 80,000–90,000 GHz). The Ba(Mg_1/3Ta_(2−2x)/3W_x/3Ti_x/3)O₃ with x = 1.0 has ɛ_r = 15.4, τ_f = −25.1 ppm/°C, Q_u × f = 35,400 GHz.     

Microwave dielectric properties of xNd(Zn1/2Ti1/2)O3–(1 − x)CaTiO3 ceramics

The microwave dielectric properties of xNd(Zn_1/2Ti_1/2)O₃–(1 − x)CaTiO₃ have been investigated. The system has been prepared by a conventional solid state ceramic route. Nd(Zn_1/2Ti_1/2)O₃ (NZT) possesses a dielectric constant (ε_r) of 32, a high quality factor (Q × f) of 170,000 GHz and a temperature coefficient of resonant frequency (τ_f) of − 42 ppm/°C. In order to produce a temperature-stable material, the addition of CaTiO₃ leads to a near-zero temperature variation of resonant frequency. In general, the microwave quality factor (Q × f) decreased as x increased and the temperature coefficient of resonant frequency (τ_f) was approximately linearly proportional to permittivity. The dielectric constant decreases from 77 to 32 as x varies from 0.2 to 1.0. The dielectric constant (ε_r) of 45, Q × f value of 56,000 (at 6 GHz) and temperature coefficient of resonant frequency (τ_f) of 0 ppm/°C were obtained for 0.5Nd(Zn_1/2Ti_1/2)O₃–0.5CaTiO₃ ceramics sintered at 1300 °C for 4 h. As the content of x increases, the highest Q × f value of 136,200 GHz for x = 0.8 is achieved at the sintering temperature 1300 °C.     

Influence of V2O5 additions to Ba(Mg1/3Ta2/3)O3 ceramics on sintering behavior and microwave dielectric properties

The microstructures and the microwave dielectric properties of barium magnesium tantalate ceramics prepared by conventional mixed oxide route have been investigated. The prepared Ba(Mg_1/3Ta_2/3)O₃ exhibited a mixture of cubic perovskite and a hexagonal superstructure with Mg and Ta showing 1:2 order in the B-site. It is found that low level doping of V₂O₅ (up to 0.5 wt.%) can significantly improve densification of the specimens and their microwave dielectric properties. The density of doped Ba(Mg_1/3Ta_2/3)O₃ ceramics can be increased beyond 95% of its theoretical value by 1500 °C-sintering, which is caused by the liquid-phase effect of V₂O₅ addition. The detected second phase Ta₂O₅ was mainly the result of V⁵⁺ substitution in the ceramics. Dielectric constant (ε_r) and temperature coefficient of resonant frequency (τ_f) were not significantly affected, while the unloaded quality factors Q were effectively promoted by V₂O₅ addition due to the increase in B-site ordering. The ε_r value of 24.1, Q×f value of 149,000 (at 10 GHz) and τ_f value of 7.2 ppm/°C were obtained for Ba(Mg_1/3Ta_2/3)O₃ ceramics with 0.25 wt.% V₂O₅ addition sintered at 1500 °C for 3 h.     

Fabrication of Nb-doped bismuth titanate thin films using nonionic block copolymer: Enhanced ferroelectric properties

Crack-free Nb-doped Bi₄Ti₃O₁₂ (Nb-BIT-p) ferroelectric thin films were fabricated utilizing nonionic block copolymer, HO(CH₂CH₂O)₂₀(CH(CH₃)CH₂O)₇₀(CH₂CH₂O)₂₀H (EO₂₀PO₇₀EO₂₀), on Pt/Ti/SiO₂/Si substrates by a processing route of metalorganic solution deposition. The Nb-BIT-p films after calcination showed only a Bi₄Ti₃O₁₂-type crystalline phase with a random orientation and small grains (< 0.4 μm). The remanent polarization (2P_r) and the coercive field (E_c) values of Nb-BIT-p capacitors were unusually high, such as 42 ± 3 μC/cm² and 72 ± 5 kV/cm, respectively, at a maximum applied field of 160 kV/cm. After 1.5 × 10¹⁰ read/write cycles with ± 8 V amplitude (160 kV/cm) at 1 MHz frequency, the 2P_r value was partially reduced, but recoverable close to the original one by repeated switching at a high field.     

Mixture of fuels approach for the solution combustion synthesis of LaAlO3 nanopowders

A modified solution combustion approach was used in the preparation of nanosize LaAlO₃ (～23.6 nm) using mixture of citric acid and oxalic acid as fuels with corresponding metal nitrates. The synthesized and calcined powders were characterized by Fourier transform infra red spectrometry (FTIR), Differential thermal analysis-Thermogravimetry analysis (DTA–TGA), X-ray diffractometry (XRD) and Transmission electron microscopy (TEM). The FTIR spectra show the lower frequency bands at 656 and 442 cm^?1corresponds to metal–oxygen bonds (possible La–O and Al–O stretching frequencies) vibrations for the perovskite structure compound. DTA confirms the formation temperature of LaAlO₃ varies between 830–835 °C. XRD results show that mixture of fuels ratio is influential on the crystallite size of the resultant powders. The average particle size of LaAlO₃-1 as determined from TEM was about 41 nm, whereas for LaAlO₃-2 and LaAlO₃-3 samples, particles are seriously aggregated.     

Evolution of different structural phases of TiO2 films with oxygen partial pressure and Fe doping and their electrical properties

We have studied the influence of oxygen partial pressure (OPP; 250 mTorr–1 × 10^?5 Torr) and Fe doping (2 and 4 at.%) on structural and electrical properties of TiO₂ thin films on LaAlO₃ substrates. X-ray photoelectron spectroscopy suggests that Fe is not in metal cluster form. It is found that the evolution of the three phases; anatase, rutile and brookite of TiO₂ as well as the magneli phase (Ti_nO_2n?1) strongly depends on the OPP and Fe doping concentration. All the films grown at 250 mTorr show insulating behavior, whereas films grown at 1 × 10^?2 and 1 × 10^?4 Torr reveal high temperature metallic to low temperature semiconducting transition. Interestingly, films deposited at 1 × 10^?5 Torr reveal charge ordering, which is contributed to the magneli phase of TiO₂. The present study suggests that functionality of TiO₂ thin film based devices can be tuned by properly selecting the OPP and dopant concentration.     

Structure and microwave dielectric characteristics of lithium-excess Ca0.6Nd0.8/3TiO3/(Li0.5Nd0.5)TiO3 ceramics

Compositions based on (1−x)Ca_0.6Nd_8/3TiO₃−x(Li_1/2Nd_1/2)TiO₃ + yLi (CNLNTx + yLi, x = 0.30–0.60, y = 0–0.05), suitable for microwave applications have been developed by systematically adding excess lithium in order to tune the microwave dielectric properties and lower sintering temperature. Addition of 0.03 excess-Li simultaneously reduced the sintering temperature and improved the relative density of sintered CNLNTx ceramics. The excess Li addition can compensate the evaporation of Li during sintering process and decrease the secondary phase content. The CNLNTx (x = 0.45) ceramics with 0.03 Li excess sintered at 1190 °C have single phase orthorhombic perovskite structure, together with the optimum combination of microwave dielectric properties of ɛ_r = 129, Q × f = 3600 GHz, τ_f = 38 ppm/°C. Obviously, excess-Li addition can efficiently decrease the sintering temperature and improve the microwave dielectric properties. The high permittivity and relatively low sintering temperatures of lithium-excess Ca_0.6Nd_0.8/3TiO₃/(Li_0.5Nd_0.5)TiO₃ ceramics are ideal for the development of low cost ultra-small dielectric loaded antenna.     

RF magnetron sputtering ferroelectric PbZr0.52Ti0.48O3 thin films with (001) preferred orientation on colossal magneto-resistive layers

Deposition by RF magnetron sputtering of PbZr_0.52Ti_0.48O₃ (PZT) ferroelectric thin films on two types of colossal magneto-resistive (CMR) oxide electrodes, La_0.67Sr_0.33MnO₃ (LSMO) and La_0.67Ca_0.33MnO₃ (LCMO), is demonstrated in this work. The multiferroic heterostructure is grown on a STO substrate, which causes a 〈001〉 preferred orientation to develop. Ferroelectric, retention of polarisation and local piezoelectric properties were measured for assessing the success of the integration from the ferroelectric point of view. Remnant polarisation P_r and coercive field E_c were found to be ∼ 40 μC/cm² and ∼ 100 kV/cm, respectively. Films presented good retention of polarisation and piezoresponse loops. These results show that ferroelectric layers with good functionality can be grown on CMR oxide films, and open the possibility of designing a piezoelectrically driven spin valve memory cell device based on this heterostructure.     

Enhanced photoluminescence and electrical properties of 0-3 type ZnO/Bi3.6Eu0.4Ti3O12 nanocomposite thin films

0-3 type ZnO/Bi_3.6Eu_0.4Ti₃O₁₂ (BEuT) nanocomposite films with ZnO nanopowders in BEuT host were prepared by chemical solution deposition. The effects of ZnO content on the structure, photoluminescence, and electrical properties of the films were investigated. The ZnO/BEuT molar ratio strongly affected the grain size and growth orientation of BEuT, dielectric and ferroelectric properties, as well as emission intensity. The nanocomposite films showed strong red emission peaks due to ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂ transitions of Eu³⁺ ions. Good electrical properties with high dielectric constant of 480 (at 1 kHz) and large remanent polarization (2P_r) of 32 μC/cm² were obtained for the nanocomposite films having a ZnO/BEuT molar ratio of 1:2. The mechanisms for enhanced photoluminescence and electric properties were discussed. The results suggest that the nanocomposite thin films are promising candidate materials for multifunctional optoelectronic devices.     

Synthesis of As-grown superconducting MgB2 thin films by sputtering method

As-grown superconducting MgB₂ thin films were prepared by very simple RF sputtering method using a single target without post-annealing process. A two-component target comprising of many small chunks of B on a Mg disk was used. The films were deposited onto polished single crystal sapphire (R-plane) or SrTiO₃ (1 1 1) substrates at rather low temperatures ranging from 100 to 110 °C. Five samples on SrTiO₃ substrate and one on sapphire showed zero resistivity at about 15 K and onset at about 20 K with measuring the resistance versus temperature (R–T curves) and the current versus voltage curves (I–V curve).