High Performance Capacitors Using BaTiO₃ Nanowires Engineered by Rigid Liquid-crystalline Polymers

Capacitors that provide high power density have attracted scientific and commercial interest, while often suffering from low energy density. Preparing a core-shell structured ceramic is regarded as a kind of effective method to improve the energy density, which is largely determined by the shell in the interfacial region. However, the current state-of-the-art of interfacial layer modification is predominantly based on utilizing flexible polymers, which are random polymer coils that collapse on the surface of any modified ceramic nanoparticles. Because of the characteristic properties of rigidity and orientation, the liquid-crystalline polymer poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PMPCS) is utilized to engineer the interfacial layer thickness on BaTiO3 nanowire surfaces via surface-initiated reversible addition-fragmentation chain transfer polymerization (RAFT) method, in this paper. As a result, a high discharged energy density of 7.5 J/cm3 and an energy efficiency of 55.1% at 300 MV/m are achieved, respectively. The findings proved that rigid liquid-crystalline polymer is a promising modifier to prepare high performance capacitors and to explore the interfacial effect in dielectric nanocomposites.</p

Interface design for high energy density polymer nanocomposites

This review provides a detailed overview on the latest developments in the design and control of the interface in polymer based composite dielectrics for energy storage applications. The methods employed for interface design in composite systems are described for a variety of filler types and morphologies, along with novel approaches employed to build hierarchical interfaces for multi-scale control of properties. Efforts to achieve a close control of interfacial properties and geometry are then described, which includes the creation of either flexible or rigid polymer interfaces, the use of liquid crystals and developing ceramic and carbon-based interfaces with tailored electrical properties. The impact of the variety of interface structures on composite polarization and energy storage capability are described, along with an overview of existing models to understand the polarization mechanisms and quantitatively assess the potential benefits of different structures for energy storage. The applications and properties of such interface-controlled materials are then explored, along with an overview of existing challenges and practical limitations. Finally, a summary and future perspectives are provided to highlight future directions of research in this growing and important area

Significantly enhanced permittivity and energy density in dielectric composites with aligned BaTiO3 lamellar structures

A significant improvement of permittivity and energy density will enable the miniaturization of dielectric capacitors and promote integration for applications in electrical power and defense systems. In this work, lamellar composite architectures are fabricated from aligned barium titanate (BaTiO3) in an epoxy resin using the freeze casting method. Due to the continuous coupling effect originating from the interconnected and highly oriented BaTiO3 particles, these composites exhibit an extremely high permittivity (εr = 1408) at 1 kHz, which is the highest value achieved in BaTiO3/polymer composites reported so far and fits well to the parallel mode of the mixing rule. A finite element model is used to investigate the local electric field distributions in the BaTiO3 lamellae under the applied electric field parallel and perpendicular to the freezing direction, respectively. A high ratio value of discharge energy density per electric field, Udis/E, ∼0.033, is achieved due to a high electric displacement of D = 15.11 μC cm−2 and a discharge energy density of Udis = 19.6 × 10−2 J cm−3 is achieved at a low electric field (6 kV mm−1). This work provides an effective strategy of designing a ceramic–polymer composite to realize high permittivity and energy density of capacitors for modern electrical and electronic industries

Enhanced photo-piezo-catalytic properties of Co-doped Ba_0.85Ca_0.15Zr_0.1(Ti_1-xCo_x)_0.9 ferroelectric ceramics for dye degradation

This paper provides a detailed evaluation of the photo-piezo-catalytic properties of lead-free Ba0.85Ca0.15Zr0.1(Ti1-xCox)0.9(BCZT-xCo,x = 0–0.025) ferroelectric ceramics prepared by a solid-state process. By control of the Co doping level, the band gap was reduced to 2.40 eV at the composition x = 0.02, which improved the generation of photo-generated charges and enhanced the photocatalytic activity. When a solution containing BCZT-0.02Co particles was subjected to both ultrasound and illumination, the degree of degradation of Rhodamine B reached 99% within 60 min, which was grater than when subjected to illumination or ultrasound alone. Examination of the dielectric properties, photoelectrochemical measurements and band energy structure of the materials provided new insights into the catalytic mechanism, where a strong coupling between piezoelectricity and photoexcitation was clearly observed. This work therefore highlights the attractive photo-piezo-catalytic properties of BCZT-xCo doped ceramics and is the first demonstration that Co substitution in these lead-free ferroelectric ceramics provides significant potential for photo-piezo-catalysis applications.</p

Enhanced photo-piezo-catalytic properties of Co-doped Ba_0.85Ca_0.15Zr_0.1(Ti_1-xCo_x)_0.9 ferroelectric ceramics for dye degradation

This paper provides a detailed evaluation of the photo-piezo-catalytic properties of lead-free Ba0.85Ca0.15Zr0.1(Ti1-xCox)0.9(BCZT-xCo,x = 0–0.025) ferroelectric ceramics prepared by a solid-state process. By control of the Co doping level, the band gap was reduced to 2.40 eV at the composition x = 0.02, which improved the generation of photo-generated charges and enhanced the photocatalytic activity. When a solution containing BCZT-0.02Co particles was subjected to both ultrasound and illumination, the degree of degradation of Rhodamine B reached 99% within 60 min, which was grater than when subjected to illumination or ultrasound alone. Examination of the dielectric properties, photoelectrochemical measurements and band energy structure of the materials provided new insights into the catalytic mechanism, where a strong coupling between piezoelectricity and photoexcitation was clearly observed. This work therefore highlights the attractive photo-piezo-catalytic properties of BCZT-xCo doped ceramics and is the first demonstration that Co substitution in these lead-free ferroelectric ceramics provides significant potential for photo-piezo-catalysis applications.</p

Evaluation of the pore morphologies for piezoelectric energy harvesting application

Piezoelectric energy harvesting has attracted significant attention in recent years due to their high-power density and potential applications for self-powered sensor networks. In comparison to dense piezoelectric ceramics, porous piezoelectric ceramics exhibit superiority due to an enhancement of piezoelectric energy harvesting figure of merit. This paper provides a detailed examination of the effect of pore morphology on the piezoelectric energy harvesting performance of porous barium calcium zirconate titanate 0.5Ba(Zr0.2 Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 (BCZT) ceramics. Three different pore morphologies of spherical, elliptical, and aligned lamellar pores were created via the burnt-out polymer spheres method and freeze casting. The relative permittivity decreased with increasing porosity volume fraction for all porous BCZT ceramics. Both experimental and simulation results demonstrate that porous BCZT ceramics with aligned lamellar pores exhibit a higher remanent polarization. The longitudinal d33 piezoelectric charge coefficient decreased with increasing porosity volume fraction for the porous ceramics with three different pore morphologies; however, the rate of decrease in d33 with porosity is slower for aligned lamellar pores, leading to the highest piezoelectric energy harvesting figure of merit. Moreover, the peak power density of porous BCZT ceramics with aligned lamellar pores is shown to reach up to 38 μW cm-2 when used as an energy harvester, which is significantly higher than that of porous BCZT ceramics with spherical or elliptical pores. This work is beneficial for the design and manufacture of porous ferroelectric materials in devices for piezoelectric energy harvesting applications.</p