Nanoindentation Study on Mechanical Properties of Nano-SiO2/Dental Resin Composites

The micro/nano-scale indentation tests were performed to explore the performance of bisphenol-α-glycidyl methacrylate (Bis-GMA)/triethylene glycol dimethacrylate (TEGDMA) dental resin composites. The effect of the filling content of nano-SiO2 particles on the mechanical properties of the dental composites was studied as well. The experimental results showed that the incorporation of the nano-SiO2 particles at low concentrations (up to 10 wt.%) can apparently increase the hardness and elastic modulus of the dental rein composites. The plasticity index indicates a best elastic recovery capability at a proper amount (4 wt.%) of the nanoparticles. Combined with the infrared spectrum, the mechanical enhancement mechanisms of the dental resin composites were analyzed.

Deep-learning enabled atomic insights into the phase transitions and nanodomain topology of lead-free(K,Na)NbO_(3) ferroelectrics

Lead-free K_(x)Na_(1-x)NbO_(3)(KNN)perovskites have garnered increasing attention due to their exceptional ferropiezoelectric properties,which are effectively tuned via polymorphic structures and domain dynamics.However,atomic insights into the underlying nanomechanisms governing the ferroelectricity of KNNs amidst varying factors such as composition,phase,and domain are still imperative.Here,we perform molecular dynamics simulations of phase transitions and domain dynamics for KNNs with various K/Na ratios(x=0.25∼1.0)by using ab-initio accuracy deep learning potential(DP).As a demonstration of its transferability,the newly developed DP model shows quantum accuracy in terms of the equation of states,elastic constants,and phonon dispersion relations for various KNbO_(3)and K_(0.5)Na_(0.5)NbO_(3).Furthermore,intricate temperature-dependent phase transitions and domain formation of KNNs are extensively and quantitatively captured.Simulations indicate that for KNNs with compositions x ranging from 0.25 to 1.0,the paraelectric-to-ferroelectric phase transition of KNNs is driven primarily by the order-disorder effect,while the displacive effect is dominant in the subsequent ferroelectric phase transitions.Specifically,flux-closure or herringbone-like nanodomain patterns arranged with 90°domain walls formed close to the experimental observations.Detailed analyses reveal that favorable 90°domain wall formation becomes more challenging with increasing Na content due to distinct oxygen octahedron distortion arising from the different ionic radii of K/Na atoms.It is envisioned that the combination of unified DP and atomistic simulations will help offer a robust solution for more accurate and efficient in silico explorations of complex structural,thermodynamic,and ferroelectric properties for relevant energy storage and conversion materials.

(Bi_(0.51)Na_(0.47))TiO_(3) based lead free ceramics with high energy density and efficiency

Dielectric ceramics with high energy storage density and energy efficiency play an important role in high power energy storage applications.In this work,lead free relaxor ferroelectric ceramics in (1-x) Bi_(0.51)Na_(0.47)TiO_(3-x)Ba(Zr_(0.3)Ti_(0.7))O_(3)(BNT-BZT100x:x=0.20,0.30,0.40 and 0.50)system are fabricated by conventional solid-state sintering method.The BNT-BZT100x ceramics are sintered dense with minimal pores,exhibiting pseudocubic symmetry and strong relaxor characteristic.A high energy storage density of 3.1 J/cm^(3) and high energy efficiency of 91% are simultaneously achieved in BNT-BZT40 ceramic with 0.1mm in thickness,at the applied electric field of 280 kV/cm.The temperature stability of the energy density is studied over temperature range of 20-160℃ ,showing minimal variation below 1.5%,together with the excellent cycling reliability(the variations of both energy density and efficiency are below 3% up to 106 cycles),making BNT-BZT40 ceramic promising candidate for high-temperature dielectric and energy storage applications.

Structure and enhanced dielectric temperature stability of BaTiO3- based ceramics by Ca ion B site-doping

Capacitor is an important part of many electronic devices,so the temperature stability as one key parameter of capacitor needs to be improved constantly for meeting the requirements of various application temperature.Here,combined with the X-ray diffraction(XRD),selected area electron diffraction(SAED)and Vienna Ab-initio Simulation Package(VASP)calculation,it was confirmed that Ca ion can substitute the Ti site in the BaTi1-xCaxO3-x[BTC100](0≤x≤0.05)ceramics synthesized by solid-phase method which greatly improved the low-temperature stability of dielectric constant.Moreover,introducing Bi3þand Zn^(2+) into BTC4 to form(1-y)BaTi0.6Ca0.04O2.96-yBi(Zn_(0.5)Ti_(0.5))O_(3)[(1-y)BTC4-yBZT](0.1≤y≤0.2)ceramics can further improve the dielectric-temperature stability by means of diffused phase transition and core-shell structure.Most importantly,the 0.85BTC4-0.15BZT ceramics with a pseudocubic perovskite structure possessed a temperature coefficient of capacitance at 25℃(TCC25℃)being less than±15%over a wide temperature range of 55℃-200℃and a temperate dielectric constant(ε=1060)and low dielectric loss(tanδ=1.5%),which measure up to the higher standard in the current capacitor industry such as X9R requirements.

Piezoelectric ceramics with high piezoelectricity and broad temperature usage range

There is a general observation that the Curie temperature and piezoelectric property of the ferroelectric ceramics can be enhanced only at the expense of each other,i.e.,higher piezoelectricity,lower Curie temperature,thus,limits their applications over broad temperature range.In this research,Sm-modified 0.15 Pb(Mg_(1/3)Nb_(2/3))O_(3)-(0.85-x)PbZrO_(3)-xPbTiO_(3) ceramics have been studied,where excellent piezoelectric coefficients d33¼720 pC/N,d_(33)*=950 pm/V and high Curie temperature T_(C)=293℃ were simultaneously achieved for x=0.42 composition by designing the morphotropic phase boundary(MPB)with local structural heterogeneity.Of particular significance is that a high thermal stability was observed with piezoelectric variation below 20%with temperature up to 280℃,demonstrating that the x=0.42 composition is a good candidate for piezoelectric application over broad temperature range where high temperature stability is required.This work provides a good paradigm for designing highperformance piezoelectric ceramics with high thermal stability via a combination of MPB and local structural heterogeneity.

Regulating energy storage performances of 0.85NaNbO_(3)-0.15Bi(Zn_(2/3)Nb_(1/3))O_(3) ceramics using BaTiO_(3)

Recently,NaNbO_(3)-based ceramics with excellent energy storage performances(ESPs)and fast chargedischarge characteristics have attracted great attention.In this case,BaTiO_(3) modified 0.85NaNbO_(3)-0.15Bi(Zn_(2/3)Nb_(1/3))O_(3)(0.85NN-0.15BZN-yBT)ceramics were designed and successfully fabricated using solid state synthesis.The discharge storage density of the ceramics increases from 1.22 J/cm^(3) at y=0-1.84 J/cm^(3) at y=8%,which is 1.5 times higher than pure 0.85NN-0.15BZN ceramics.This ceramic reveals excellent temperature stability up to 150℃,good discharge cycling after 10^(5) cycles and high discharge speed of 2.0μs,broadening the scope of NaNbO_(3)-based ceramics for energy storage applications.

Structure and electrical properties of ternary BiFeO_(3)-BaTiO_(3)-PbTiO_(3) high-temperature piezoceramics

In the current work,the bulk ternary(0.85-x)BiFeO3-xBaTiO3-0.15PbTiO3(BF-BTx-PT,x=0.08-0.35)system has been studied as a potential high-temperature piezoceramics.Samples with various content of BT were prepared via solid-state route,and pure perovskite phase was confirmed by X-ray diffraction.The temperature dependence of dielectric constants confirmed the decrease of Curie temperature with increasing BT content.It was found that the morphotropic phase boundary(MPB)composition of BF-BTx-PT ceramics was in the vicinity of x=0.15,which exhibits optimal properties with piezoelectric constant d33 of 60 pC/N,high Curie temperature of 550℃,and low sintering temperature of 920℃.Measurements also showed that the depoling temperature was 300℃,about 150℃higher than that of commercialized PZT ceramics,which indicated good temperature stability.BF-BTx-PT ceramics are promising candidates for high temperature applications.

Grain boundary effects on piezoelectric properties of the core–shell-structured BaTiO_(3)@TiO_(2) ceramics

Grain boundary effect on BaTiO_(3) has been widely investigated for several decades.However,all of them tailored the grain boundary by grain size of BaTiO_(3).In this case,a direct way was introduced to modify the grain boundary by coating technique to investigate the role of grain boundary in ferroelectric materials.Nonferroelectric phase TiO_(2) was employed to investigate grain boundary effects on the electrical properties of BaTiO3 piezoelectric ceramics.TiO_(2) coating can result in the reduction of piezoelectric and ferroelectric properties and the annealing process in oxygen can increase piezoelectric behavior of pure BaTiO3 due to valence state of Ti ions while that remains for Ti-modified composition possibly due to the increased grain boundary effect by impedance analysis.Compared with ferroelectric grain,grain boundary plays a critical role to impact the electrical properties of perovskite-type ferroelectric materials.

INFLUENCE OF CaF_(2)-4LiF ADDITIVE ON SINTERING AND ENERGY STORAGE PERFORMANCE OF SrTiO_(3)CERAMICS

The CaF_(2)-4LiF additive was added into SrTiO_(3)ceramics in order to decrease the sintering temperature for compact pulse power application.The crystalline structure,microstructure and energy storage performance of sintered ceramics were studied.Incorporating CaF_(2)-4LiF additive to SrTiO_(3)ceramics contributes to a notably enhancement of the energy storage density.The great enhancement in energy storage density occurred due to the notable increase in breakdown strength and the refinement of microstructure.With 2 at%additive,the samples exhibited an average breakdown strength of 31.8kV/mm,and an energy storage density of 1.212 J/cm^(3)which is about 1.4 times higher than pure SrTiO_(3).