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The antiferroelectric (Pb0.985Sm0.01) (Zr1-xTix)O3 (Ti-PSZO) thin films were synthesized on Pt(111)/Ti/SiO2/Si substrates using a chemical solution deposition method. The films were crystallized in the perovskite phase with a preferential orientation along (111) direction. With Ti doping in PSZO, a gradual transformation from antiferroelectric to ferroelectric phase transition was noticed at room temperature owing to the Ti doping induced lattice distortion. The phase transition has been confirmed through the P - E hysteresis loops, X-ray diffraction (peak shifting), capacitance-voltage measurements, and Raman scattering analysis. The thin film with Ti = 0.15 doping displayed a ferroelectric behavior with high dielectric constant and large dielectric tunability of about 62%. Also, Ti doping altered the Curie temperature (Tc) and enhanced the order of dielectric diffuseness. It is believed that Ti-doping in PSZO is an effective way to induce an antiferroelectric - ferroelectric phase transition and to tailor the electrical characteristics of PSZO thin films.

Excellent dielectric frequency, bias, and temperature stability of bismuth silicate (Bi2SiO5, BSO) thin films with a low dielectric loss has been obtained in this study. The thin films were prepared on Pt/Ti/SiO2/Si substrates by a chemical solution deposition method at a relatively low annealing temperature of 500 °C. The BSO films have a preferred growth along (200) orientation with dense fine-grained surface morphology. The dielectric constant and dielectric loss of the thin film annealed at 500 °C are 57 and 0.01, respectively, at 100 kHz, with little change between 1 kHz and 100 kHz and in the bias electric field range between −250 kV/cm and 250 kV/cm, indicating that the thin film exhibits a low dielectric loss as well as excellent frequency and bias field stability. The dielectric-temperature measurements confirmed that the BSO thin film annealed at 500 °C also has good temperature stability between 150 K and 450 K. Our results suggest that the BSO thin films have potential applications in the next-generation integrated capacitors.

Antiferroelectric Sm-doped PbZrO3 (PSZO) thin films were prepared on Pt(111)/Ti/SiO2/Si substrates using a chemical solution deposition method. The effects of Sm doping concentration on structural, morphology, dielectric, antiferroelectric, and energy storage characteristics of PSZO thin films were investigated. With Sm doping, all the thin films were crystallized in perovskite phase along with a strong (111)- preferential orientation. It is found that Sm doping significantly altered the Curie temperature (Tc) and electric field-induced phase switching of the films. The PSZO film with Sm = 0.01 exhibited a maximum polarization of 53.7 μC/cm2, an energy storage density of 17.1 J/cm3 at ~444 kV/cm, and a dielectric constant of 175 at 1 kHz. The improved energy storage performance was attributed to high (111) degree of preferred orientation and site occupation of Sm ions.

We report the coexistence of resistive switching and magnetism modulation in the Pt/Co3O4/Pt devices, where the effects of thermal annealing and film thickness on the resistive and magnetization switching were investigated. The sol-gel derived nanocrystalline Co3O4 thin films obtained crack-free surface and crystallized cubic spinel structure. The 110 nm Co3O4 film based device annealed at 600 °C exhibited optimum resistive switching parameters. From I–V curves fitting and temperature dependent resistance, the conduction mechanism in the high-voltage region of high resistance state was dominated by Schottky emission. Magnetization-magnetic field loops demonstrated the ferromagnetic behaviors of the Co3O4 thin films. Multilevel saturation magnetization of the Co3O4 thin films can be easily realized by tuning the resistance states. Physical resistive switching mechanism can be attributed to the rejuvenation and annihilation of conductive filament consisting of oxygen vacancies. Results suggest that Pt/Co3O4/Pt device shows promising applications in the multifunctional electromagnetic integrated devices.

Structure, dielectric, ferroelectric, fatigue, and photoluminescent properties of Bi3.86−kSm0.14LakTi3O12 (BSLT) thin films synthesized by sol–gel method were investigated. The XRD analysis indicated that the BSLT thin films formed single phase orthorhombic structure, and orthorhombic distortion was found to increase with increasing lanthanum doping content. Raman spectra revealed that BSLT thin films have significantly structure distorted because of La3+ doping, which is consistent with XRD results. Increasing La substitution results in improvement in dielectric and ferroelectric properties of BSLT thin films due to distorted structure and defects reduction. The films show almost fatigue-free ferroelectric polarization behavior at room temperature. Besides, the BSLT thin films show orange-red color emission at 604 nm and long florescence lifetime (about 0.75 ms). This study indicates that the thin films with an appropriate doping concentration of Sm3+, La3+ ions may have potential applications in multifunctional optoelectronic devices.

Sol-gel method was used to prepare the Pr3+ ions-doped (1-x)Na0.5Bi0.5TiO3-xCaTiO3 (Pr-NBT-xCTO) (x = 0, 0.04, 0.06, 0.08, 0.1, 0.12, and 0.16) thin films on Pt/Ti/SiO2/Si and fused silicon substrates. The structure phase of thin films was evolving from rhombohedral (R3c) to orthorhombic (Pnma) with increasing CTO content. Owing to the morphotropic phase boundary (MPB), the improved ferroelectric and dielectric properties were obtained at x = 0.06–0.1. The MPB was formed from the concomitant phase of rhombohedral (R3c) and orthorhombic (Pnma). The Pr-NBT-0.08CTO thin film showed the best ferroelectric and dielectric properties, as well as strong relaxor behavior (the diffusion factor is γ = 1.79). In addition, all the films exhibited strong red emission as excited by UV light, and wide optical band-gap (3.44–3.47 eV), which might be influenced by grain size and structural variation. Our results indicate that Pr-NBT-xCTO thin films may have potential applications in ferroelectric-luminescence multifunctional optoelectronic devices.

Spinel Co3O4 thin films were synthesized using a sol–gel technique to study the annealing atmosphere effect on resistive switching (RS) and magnetic modulation properties. Compared with oxygen and air annealed Pt/Co3O4/Pt stacks, the nitrogen annealed Pt/Co3O4/Pt stack shows optimal switching parameters such as a lower forming voltage, uniform distribution of switching voltages, excellent cycle-to-cycle endurance (>800 cycles), and good data retention. Improvement in switching parameters is ascribed to the formation of confined conducting filaments (CFs) which are composed of oxygen vacancies. From the analysis of current–voltage characteristics and their temperature dependence, the carrier transport mechanism in the high-field region of the high resistance state was dominated by Schottky emission. Besides, temperature dependent resistance and magnetization variations revealed that the physical mechanism of RS can be explained based on the formation and rupture of oxygen vacancy based CFs. In addition, multilevel saturation magnetization under different resistance states is attributed to the variation of oxygen vacancy concentration accompanied with the changes in the valence state of cations. Results suggested that using a nitrogen annealing atmosphere to anneal the thin films is a feasible approach to improve RS parameters and enhance the magnetic properties of Co3O4 thin film, which shows promising applications to design multifunctional electro-magnetic coupling nonvolatile memory devices.

In this Letter, spinel ferrite NiFe2O4 films prepared through pulsed laser deposition are used to fabricate Pt/NiFe2O4/Pt devices with the coexistence of unipolar resistive switching (URS) and bipolar resistive switching (BRS). The device demonstrated nonvolatile and stable resistive switching (RS) properties under URS and BRS modes. The current–voltage (I–V) fitting analysis and temperature dependence measurements suggested that one Pt/NiFe2O4/Pt RRAM cell follows two significantly different RS and carrier transport mechanisms under URS and BRS modes. Under URS mode, the carrier mechanism alternates between the high resistance state (HRS) with Schottky emission and low resistance state (LRS) with the Ohmic mechanism. In contrast, under BRS mode, carrier transport at HRS and LRS is dominated by space-charge-limited current and nearest-neighboring hopping, respectively. Finally, a physical model, combining oxygen ion (O2−) migration and electric field distribution simulated by COMSOL Multiphysics, is proposed to further clarify the coexistence of two distinct RS and carrier transport mechanisms in the single Pt/NiFe2O4/Pt RRAM device.

Piezoelectric effect, commonly known as a change in electric polarization in piezoelectric/ferroelectric materials under mechanical stress, is extensively employed as a driving force for the catalytic degradation of organic pollutants. However, the relationship between electric polarization and piezocatalytic activity is still unclear. In this work, we investigated the role of ferroelectric polarization in the piezocatalytic activity of BaTiO3 nanoparticles through annealing BaTiO3 at different temperatures or poling BaTiO3 at different electric fields. The BaTiO3 nanoparticles annealed at 800 °C exhibit effectively enhanced piezocatalytic activity compared with those annealed at other temperatures. The polycrystalline particles annealed at higher temperatures exhibit a greatly reduced catalytic activity. After poling, the piezocatalytic activity of the polycrystalline BaTiO3 particles was obviously improved. In addition, we identified the free radical species and the intermediate products of the catalytic reaction. We also well-explained the dependence of electric polarization in the BaTiO3 piezocatalyst on annealing temperature and ultrasonic vibration theoretically. Our study indicates that increasing ferroelectric polarization (but not crystallite size) can effectively enhance the piezocatalytic activity. We believe that the present work provides a clear understanding of the role of ferroelectric polarization in piezocatalysis.

Spinel Co

Nanocrystalline bilayer composite MnO2/Co3O4 thin films were fabricated by a simple chemical solution deposition method to investigate the resistive and magnetization switching properties. Compared with pure Co3O4 thin films device, bilayer MnO2/Co3O4 thin films device exhibits enhancement in resistive switching (RS) and magnetization modulation, such as uniform SET and RESET voltages, stable cycle-to-cycle switching endurance (>2 × 103 cycles), good data retention time (>104 s), and RS induced magnetization switching (∼63%). Through the analysis of fitting current-voltage (I–V) curves and temperature-dependent resistance, it demonstrated that Schottky emission conduction is dominated at high resistance state of the devices. Enhancement in RS performance can be attributed to the growth and dissolution of confined conductive filaments which are composed of Mn atoms and oxygen vacancies, evidenced by temperature dependence and magnetization switching at different resistance states. The physical relevancy between RS and magnetic switching involves in the creation and annihilation of conductive filaments, associated with the reversible conversion of cation valence state (Co2+ and Co3+, Mn ions and Mn atoms). Results suggest that by introducing a thin MnO2 inserting layer, Co3O4 based device shows promising applications for nonvolatile RS memory and multifunctional electromagnetic coupling device.

In this work, large-area ferrite thin films of ferromagnetic yttrium iron garnet (Y3Fe5O12, YIG) were synthesized on Pt/Ti/SiO2/Si (Pt) substrates by a sol-gel method to investigate the resistive and magnetization switching properties. The synthesized YIG thin films acquire a single garnet structure. The Pt/YIG/Pt stack illustrates unipolar resistive switching behavior with excellent switching uniformity, large memory window (102), stable cycle-to-cycle endurance, and good data storage retention (104 s). The ~46% saturation magnetization variation could be realized via the conversion between high and low resistance states by manipulating the electric field. Schottky emission is governed in the high-field region for the high resistance state. Temperature dependence of resistance and magnetization variation confirms that oxygen vacancies conductive filament model and valence state change (Fe2+ and Fe3+) are responsible for the resistive and magnetization switching mechanisms. These results indicate that YIG ferrite based stack is suitable to design the electro-magnetic coupling multifunctional nonvolatile memory devices.

Pr3+-doped Na0.5Bi0.5TiO3 (Pr-NBT) thin films with different preferred orientations including random, (100), and (110) orientations were prepared on Pt/Ti/SiO2/Si substrates by a chemical solution deposition method combining with a rapid thermal annealing. Effects of the crystallographic orientation on the ferroelectric and dielectric properties of Pr-NBT thin films were investigated. XRD patterns revealed that the preferential orientation degrees of (100)- and (110)-oriented Pr-NBT thin films were 97% and 69%, respectively. The (100)-oriented Pr-NBT thin film has a higher dielectric constant of 1035 compared to the (110)- and randomly oriented ones. Furthermore, a large remnant polarization (2Pr = 31 µC/cm2) was obtained from the highly (100)-oriented Pr-NBT thin film, which is 1.55 times larger than that of the randomly oriented film. The quantitative relationship in dielectric constants between the (100)-, (110)-oriented, and randomly oriented Pr-NBT thin films was calculated using the dipole azimuth model. The calculated result was consistent with experimental measurements. The optimal dielectric tunable property (tunability = 40.8%, FoM = 10.2) is obtained from (100)-oriented films. The highly (100)-oriented Pr-NBT lead-free thin film is promising for use in integrated microelectronic devices.

High energy heavy ion irradiation-induced modification of high quality crystalline GeO2 thin films grown at different substrate temperatures ranging from 100 to 500 °C using pulsed laser deposition has been investigated. The pristine films were irradiated with 100 MeV Ag7+ ions at fixed fluence of 1 × 1013 ions/cm2. These pristine and irradiated films have been characterized using X-ray diffraction, atomic force microscopy, Raman spectroscopy, Fourier transform infrared and photoluminescence spectroscopy. The XRD and Raman results of pristine films confirm the formation of hexagonal structure of GeO2 films, whereas the irradiation eliminates all the peaks except major GeO2 peak of (101) plane. It is evident from the XRD results that crystallite size changes with substrate temperature and SHI irradiation. The surface morphology of films was studied by AFM. The functional group of pristine and irradiated films was investigated by IR transmission spectra. Pristine films exhibited strong photoluminescence around 342 and 470 nm due to oxygen defects and a red shift in the PL bands is observed after irradiation. Possible mechanism of tuning structural and optical properties of pristine as well as irradiated GeO2 films with substrate temperature and ion beam irradiation has been reported in detail.

Oxygen vacancies derived resistive and magnetic switching, was demonstrated in facile solution-processed Au-Co3O4 nanocomposite thin films, in terms of optimum Au content. The metal element introduced is a unique way to create the optimum amount of oxygen vacancies in the dielectric films even in the absence of electrochemically active electrodes. Compared with pure Co3O4 based device, the RRAM device with Au additives showed bipolar switching behavior with uniform Set/Reset voltages, enhanced endurance of >103 cycles, and stable time-dependent resistances up to 104 s. The introduction of Au nanoparticles caused the oxygen vacancies based confined filament growth for optimum switching uniformity and stability. Results showed that Ohmic conduction was dominant at LRS and Schottky emission was dominated at HRS of the devices. Temperature dependence and magnetization change of various resistance states revealed that resistive and magnetic switching was due to the formation and rupture of conductive filaments of Au atoms confined oxygen vacancies with the conversion of cation valence states (Co2+ and Co3+). The present study suggests that Au-Co3O4 nanocomposite thin films have a potential for future multifunctional electromagnetic integrated device applications.

The microwave dielectric properties of CeO(2) nanoparticles (0.5, 1.0 & 1.5wt%) doped Mg(2)(TiO(4)(MTO) ceramics have been investigated at cryogenic temperatures. The XRD patterns of the samples were refined using the full proof program reveal the inverse spinel structure without any secondary phases. The addition of CeO(2) nanoparticles lowered the sintering temperature with enhancement in density and grain size as compared to pure MTO ceramics. This is attributed to the higher sintering velocity of the fine particles. Further, the microwave dielectric properties of the MTO ceramics were measured at cryogenic temperatures in the temperature range of 6.5-295 K. It is observed that the loss tangent (tanδ) of all the samples increased with temperature. However, the CeO(2) nanoparticles doped MTO ceramics manifested lower loss tangents as compared to the pure MTO ceramics. The loss tangents of the pure and MTO ceramics doped with 1.5 wt% of CeO(2) nanoparticles measured at 6.5K are found to be 6.6x10^-5 and 5.4x10^-5, respectively. The addition of CeO(2) nanoparticles did not cause any changes on the temperature stability of the MTO ceramics at cryogenic temperatures. On the other hand, the temperature coefficient of the permittivity increased with rise in temperature and with the wt% of CeO(2) nanoparticles. The obtained lower loss tangent values at cryogenic temperatures can be attributed to the decrease in both intrinsic and extrinsic losses in the MTO ceramics.

MgTiO 3 (MTO) ceramics have been prepared by the conventional solid-state reaction method. The effects of CeO 2 nanoparticles up to 1.5 wt% as a sintering aid and annealing temperature on the crystal structure, microstructure and microwave dielectric properties of MTO ceramics were investigated. It is found that the addition of CeO 2 nanoparticles to the MTO ceramics leads to improvement in the relative density, reduction in sintering temperature. However, Q × f o values are found to decrease marginally. The driving forces for the improved sintering process are the large surface energy of CeO 2 nanoparticles and their defect energy, which are activated during the sintering process. The addition of CeO 2 nanoparticles does not change the dielectric constant ( e r ), and the unloaded quality factor ( Q u ) but the τ f values are altered significantly. The annealing temperatures of the pure MTO ceramics and MTO+ x CeO 2 ( x =0.5, 1.0 and 1.5 wt%) were optimized. The samples annealed at 1100 °C for 48 h exhibit the best microwave dielectric properties. The maximum value of Q × f o for the pure MTO was achieved by sintering at1400 °C and significantly such maximum value was achieved in x =0.5 wt% sample by sintering at 1300 °C itself. The values of Q × f o are in the range of 52250–140800 GHz. Pure MTO ceramics sintered at 1400 °C and annealed at 1100 °C for 48 h exhibit the best microwave dielectric properties ( e r =17.21, Q × ƒ o =165500 GHz). The observed results are correlated to the reduction in oxygen vacancies, relaxation of strain during annealing, increase in grain size and relative densities.