High recoverable energy storage density of Na_(0.5)Bi_(0.5)TiO_(3) lead-free ceramics modified by Bi(Mg_(0.5)Hf_(0.5))O_(3)

Enhancing the availability and reliability of dielectric ceramic energy storage devices is of great importance.In this work,(1-x)Na_(0.5)Bi_(0.5)TiO_(3)-xBi(Mg_(0.5)Hf_(0.5))O_(3)(NBT-xBMH)lead-free ceramics were created utilizing a solid-state reaction technique.All NBT-xBMH ceramics have a single perovskite structure.With increasing BMH doping,the grain size shrinks drastically,which greatly enhances the breakdown electric field(310 kV/cm at x=0.25).Additionally,the relaxation behaviors of NBT-xBMH ceramics with high BMH content are more remarkable.Among all designed components,the NBT-0.25BMH ceramic exhibits the best energy storage performance with a high Wrec of 4.63 J/cm^(3) and anηof 75.1%at 310 kV/cm.The NBT-0.25BMH ceramic has exceptional resistance to fluctuations in both frequency(5-500 Hz)and temperature(30-100°C).Charge-discharge test shows that the NBT-0.25BMH ceramic has a quick discharge rate(t0.9<110 ns).With these properties,the NBT-0.25BMH ceramic may have applications in microdevices as well as in ultra-high power electronic systems.

Mechanical-electrical-chemical coupling study on the stabilization of a hafnia-based ferroelectric phase

The metastable polar orthorhombic phase is believed to be the origin of the ferroelectricity of hafnia-based films.The adjustment of stain,oxygen vacancies and dopant during film deposition and the wake-up electric cycling are common strategies to induce the ferroelectricity in hafnia.However,none of them could independently render the ferroelectric phase to be the most stable phase from the theoretical calculation results.The exact external conditions to stabilize orthorhombic phase still remain elusive.In this paper,we investigate the effects of the type,distribution,concentration,and charge state characteristics of oxygen vacancies and the uniaxial strain on the crystal’energy,dielectric constant and spontaneous polarization(Ps);In addition,the impact of the applied electric field parallel to the Ps on the crystal’energy is explored by first-principles calculations.It is challenging to independently stabilize the ferroelectric phase of hafnia-based films by a single component owing to the rather strict conditions.Surprisingly,the ferroelectricity can be easily obtained when simultaneously considering the effects of oxygen vacancies,uniaxial strain,and applied electric fields,suggesting the extremely important mechanical-electrical-chemical coupling effects.This work provides an explanation for the typical wake-up phenomenon in hafnia and a guidance for film applications.

Resistive switching and optical properties of strontium ferrate titanate thin film prepared via chemical solution deposition

The polycrystalline strontium ferrate titanate(SrFe_(0.1)Ti_(0.9)O_(3),SFTO)thin films have been successfully prepared by chemical solution method.By analyzing the current-voltage(I-V)characteristics,we discuss the conduction mechanism of SFTO.It is found that the number of oxygen vacancy defects is increased by Fe ion doping,making SFTO be with better resistive switching property.Fe ion doping can also enhance the absorption of strontium titanate to be exposed to visible light,which is associated with the change of energy band.The band gap width(2.84 eV)of SFTO films is figured out,which is less than that of pure strontium titanate.Due to more oxygen vacancy defects caused by Fe ion doping,the band gap width of strontium titanate was reduced slightly.The defect types of SFTO thin films can be determined by electron paramagnetic resonance spectroscopy.In addition,we analyzed the energy band and state density of SFTO by first-principles calculation based on density functional theory,and found that Fe ion doping can reduce the band gap width of strontium titanate with micro-regulation on the band structure.A chemical state of SFTO was analyzed by X-ray photo electron spectroscopy.At the same time,the structure and morphology of SFTO were characterized by X-ray diffraction and scanning electron microscope.This study deepens further understanding of the influence of Fe ion doping on the structure and properties of strontium ferrate titanate,which is expected to be a functional thin film material for memristor devices.