Universal converse flexoelectricity in dielectric materials via varying electric field direction

Flexoelectricity is a symmetry independent electromechanical cou-pling phenomenon that outperforms piezoelectricity at micro and nanoscales due to its size-dependent behavior arising from gradi-ent terms in its constitutive relations.However,due to this gradient term flexoelectricity,to exhibit itself,requires specially designed geometry or material composition of the dielectric material.First of its kind,the present study put forward a novel strategy of achieving electric field gradient and thereby converse flexoelectri-city,independent of geometry and material composition of the material.The spatial variation of the electric field is established inside the dielectric material,Ba_(0.67)Sr_(0.33)TiO_(3)(BST),by manipulating electrical boundary conditions.Three unique patterns of electrode placement are suggested to achieve this spatial variation.This varying direction of electric field gives rise to electric field gradient,the prerequisite of converse flexoelectricity.A multi-physics cou-pling based theoretical framework is established to solve the flexo-electric actuation by employing isogeometric analysis(IGA).Electromechanically coupled equations of flexoelectricity are solved to obtain the electric field distribution and the resulting displace-ments thereby.The maximum displacements of 0.2 nm and 2.36 nm are obtained with patterns I and II,respectively,while pattern III can yield up to 85 nm of maximum displacement.

Piezoelectric material selection for transducers under fuzzy environment

Piezoelectric ceramics are extensively investigated materials for transducer application.The selection of optimal piezoelectric material for this particular application is a tedious task.It depends upon various physical properties,including piezoelectric charge coefficient(d33),electromechanical coupling factor(K_(p)),dielectric constant(ε_(r)),and dielectric loss(tanδ).The classical multiple attribute decision making(MADM)can be used for decision making if these properties are known precisely.However,these properties cannot be expressed by exact numerical values,since they are dependent upon the microstructure and fabrication process.Fuzzy-based MADM approaches can be helpful in such cases.In this paper,we have determined the ranks and rank indices(for degree of closeness)of important piezoelectric materials using fuzzy VlseKriterijumska Optimisacija I Kompromisno Resenje(VIKOR)technique.PLZT(8/65/35)((Pb_(1-x)La_(x))(Zr_(y)Ti_(1-y))O_(3))and KNN-LT-LS((K_(0.44)Na_(0.52)Li_(0.04))-(Nb0_(.84)Ta_(0.10)Sb_(0.06))O_(3))consecutively are found to be the top-rank piezoelectric ceramics.This indicates that KNN-LT-LS can be used on behalf of lead-based piezo-ceramics.

Piezoelectric materials selection for sensor applications using finite element and multiple attribute decision-making approaches

This paper examines the selection and performance evaluation of a variety of piezoelectric materials for cantilever-based sensor applications.The finite element analysis method is implemented to evaluate the relative importance of materials properties such as Young's Modulus(E),piezoelectric stress constants(e_(31)),dielectric constant(ε)and Poisson's ratio(ν)for cantilever-based sensor applications.An analytic hierarchy process(AHP)is used to assign weights to the properties that are studied for the sensor structure under study.A technique for order preference by similarity to ideal solution(TOPSIS)is used to rank the performance of the piezoelectric materials in the context of sensor voltage outputs.The ranking achieved by the TOPSIS analysis is in good agreement with the results obtained from finite element method simulation.The numerical simulations show that K_(0.5)Na_(0.5)NbO_(3)-LiSbO_(3)(KNN-LS)materials family is important for sensor application.Young's modulus(E)is most influencing material's property followed by piezoelectric constant(e_(31)),dielectric constant(ε)and Poisson's ratio(ν)for cantilever-based piezoelectric sensor applications.

Effect of Sr_(2) TiMnO_(6) fillers on mechanical, dielectric and thermal behaviour of PMMA polymer

Composites of poly(methyl methacrylate)(PMMA)and Sr_(2) TiMnO_(6)(STMO)were fabricated via melt mixing followed by hot pressing technique.These were characterized using X-ray diffraction(XRD),thermo gravimetric analysis(TGA),differential scanning calorimetry(DSC),thermo mechanical analysis(TMA)and impedance analyser for their structural,thermal and dielectric properties.The coefficient of thermal expansion(CTE)was measured between 40℃ and 100℃ for pure PMMA is 115.2ppm/℃,which was decreased to 78.58ppm/℃ when the STMO content was increased to 50 wt.%in PMMA.There was no difference in the glass transition(T g)temperature of the PMMA polymer and their composites.However,the FTIR analysis indicated possible interaction between the PMMA and STMO.The density and the hardness were increased as the STMO content increased in the PMMA matrix.Permittivity was found to be as high as 30.9 at 100Hz for the PMMAþSTMO-50 wt.%composites,indicating the possibility of using these materials for capacitor applications.The thermal stability of polymer was enhanced by incorporation of STMO fillers.

Giant energy harvesting potential in(100)-oriented 0.68PbMg_(1/3)Nb_(2/3)O_(3)-0.32PbTiO_(3)with Pb(Zr_(0.3)Ti_(0.7))O_(3)/PbO_(x)buffer layer and(001)-oriented 0.67PbMg_(1/3)Nb_(2/3)O_(3)-0.33PbTiO_(3)thin films

This work emphasis on the competence of(100)-oriented PMN–PT buffer layered(0.68PbMg_(1/3)Nb_(2/3)O_(3)–0.32PbTiO_(3)with Pb(Zr_(0.3)Ti_(0.7))O_(3)/PbO_(x)buffer layer)and(001)-oriented PMN–PT(0.67PbMg_(1/3)Nb_(2/3)O_(3)–0.33PbTiO_(3))for low grade thermal energy harvesting using Olsen cycle.Our analysis(based on well-reported experiments in literature)reveals that these films show colossal energy harnessing possibility.Both the films are found to have maximum harnessable energy densities(PMN–PT buffer layered:8 MJ/m^(3);PMN–PT:6.5 MJ/m^(3))in identical ambient conditions of 30–150℃and 0–600 kV/cm.This energy harnessing plausibility is found to be nearly five times higher than the previously reported values to date.

ELECTRICAL TRANSPORT STUDIES IN 3Na_(2)O-6:5B_(2)O_(3) GLASSES

Transparent 3Na_(2)O-6:5B_(2)O_(3)(NBO)glasses were fabricated via the conventional melt-quenching technique.X-ray powder difraction(XRD)combined with Differential Scanning Calorimetric(DSC)studies carried out on the as-quenched samples confirmed their amorphous and glassy nature,respectively.The frequency and temperature dependent of the dielectric constant,electric modulus and electrical conductivity of the transparent NBO glasses were investigated in the 100 Hz-10 MHz frequency range.The electrical modulus and conductivity data have been rationalized using Jonscher's universal law.The bulk dc conductivity at various temperatures was extracted from the electrical relaxation data.The activation energy associated with dc conduc-tivity is 0.52±0.01 eV,which is ascribed to the motion of Na^(+)ions in the glass matrix.