Ferroelectric elements of high-power electrical generators, utilizing the ability of ferroelectric materials to produce electric charge under mechanical stress, are subjected to either high-pressure shock or moderate-pressure impact loading. The results are reported herein on experimental investigations of a different mode for the generation of a high electric charge density, one that utilizes pre-compressed ferroelectric ceramics. Hard PZT 52/48 (Navy Type I/PZT-4) ferroelectric ceramic specimens were subjected to static uniaxial compressive stress parallel to polarization. At the moment of operation, the output terminals of the specimens were connected to an external circuit, and the applied stress was quickly removed, resulting in the generation of electric charge. The results indicate that this new method for harvesting electric charge from pre-compressed ferroelectrics produced a surface charge density of 7.4 μC/cm2 upon release of 71 MPa compressive stress, significantly higher than that calculated using the linear piezoelectric charge coefficient d33. Under pre-compressive stresses exceeding 3 MPa, d33 exhibits a nonlinear increase. Higher order terms were introduced into the electro-mechanically coupled constitutive law to model the observed behavior. No degradation of piezoelectric properties or mechanical failure of the ferroelectric specimens was detected over the full range of stress investigated, 0.4–71 MPa. Multi–element ferroelectric modules had no significant electric charge losses after 168 h of 35.4 MPa compression. Therefore, pre-compressed ferroelectrics are capable of producing large electric charges during millisecond time intervals and can be used as high-power energy storage devices.

The dependence of the dielectric permittivity of ferroelectric materials on electric field magnitude impacts the performance of ferroelectric devices. In a ferroelectric generator, a shock wave travels through the ferroelectric element and depolarizes it, and surface charges are released from the element electrodes, resulting in the generation of a megawatt power level for several microseconds. The dielectric properties of the compressed and uncompressed zones of the ferroelectric element affect the generated voltage and energy. The results of previous studies indicate that the low-field dielectric permittivity of poled Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 (PZT 95/5) ferroelectrics in the uncompressed zone differs significantly from the high-field permittivity. Herein, the results are presented from the experimental investigation of the high-field permittivity of poled uncompressed PZT 95/5 ferroelectric ceramics and films, PZT 52/48 ferroelectric ceramics, and rhombohedral 0.27Pb(In1/2Nb1/2)O3–0.47Pb(Mg1/3Nb2/3)O3–0.26PbTiO3 (0.27PIN-PMN-0.26PT) and 0.68Pb(Mg1/3Nb2/3)O3–0.32PbTiO3 (0.68PMN-0.32PT) ferroelectric single crystals. The dependences of the permittivity on the electric field were determined using a pulsed electric field ranging from 0.1 to 10 kV/mm. The data indicate that the application of a pulsed high electric field results in a fourfold increase in the relative permittivity of PZT 95/5 ceramics and films over the small signal value (from 300 to 1200), and a threefold increase in the permittivity of single-domain [111]c cut and poled 0.27PIN-PMN-0.26PT crystals (from 700 to 2100), while a high electric field does not have a significant impact on the permittivity of PZT 52/48 ceramics or 0.27PIN-PMN-0.26PT and 0.68PMN-0.32PT crystals cut and poled in the domain engineered [001]c or [011]c direction.

The unique ability of ferroelectrics to generate high voltage under shock loading is limited by electrical breakdown within the shock-compressed ferroelectric material. Breakdown is a hybrid process of initiation and growth. The possible mechanisms of electrical breakdown in ferroelectric films and bulk ceramics subjected to high-pressure shock loading are discussed and experiments designed to elucidate which mechanisms govern breakdown. Gigapascal shock loading experiments were performed on poled Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 ferroelectric film specimens in the range of 32–156 μm thickness to determine the dependence of the breakdown field on thickness and on film specimens in the range of 4–16 mm length to determine the dependence of the breakdown field on the duration of shock compression. The resulting breakdown-field vs thickness and breakdown-field vs shock transit time dependencies are consistent with a hybrid electron emission initiation and Joule heating microchannel growth mechanism. Further analysis of data previously obtained on shock-compressed 0.27Pb(In1/2Nb1/2)O3–0.47Pb(Mg1/3Nb2/3)O3–0.26PbTiO3 ferrvoelectric single crystals and Pb(Zr0.65Ti0.35)O3, Pb0.99(Zr0.52Ti0.48)0.99Nb0.01O3, Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 bulk ceramics is consistent with this dual mechanism. It appears that neither chemical composition nor microstructure (single crystal vs polycrystalline) of the ferroelectric material has a significant effect on the breakdown mechanism in shocked ferroelectrics.

The results are reported herein of experimental investigations of the mechanism of electric breakdown and the generation of high voltage and energy by shock-compressed rhombohedral (1-y-x)Pb(In1/2Nb1/2)O3-yPb(Mg1/3Nb2/3)O3-xPbTiO3 (PIN-PMN-PT) ferroelectric single crystals cut and poled along the [111]c crystallographic direction. PIN-PMN-PT crystals were shock-compressed in a direction perpendicular to the polarization, in either the [11¯0]c or [112¯]c crystallographic directions. Our experiments demonstrated that shocked crystals with thicknesses ranging from 1 to 5 mm are capable of producing high voltage amplitudes of 9–37 kV, with the amplitudes being directly proportional to the crystal thickness. The experimental results indicate that the shock loading direction does not have a significant effect on the generated voltage amplitude. The important finding is that the breakdown fields of adiabatically compressed crystals strongly depend on the crystal thicknesses, and this dependence obeys a power law similar to the one for solid dielectrics at ambient conditions. We found that high electric fields have significant impacts on the dielectric permittivity of poled PIN-PMN-PT crystals and a corresponding effect on the generated energy density. Our experimental results made it possible to determine the relationship between the energy density generated by crystals under shock loading and the crystal thickness. The energy density generated by shocked PIN-PMN-PT crystals is greater by a factor of three than that for high-energy-density Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 ferroelectric ceramics currently used in high-power systems, making these crystals very promising ferroelectric materials for high-power applications.

Compact autonomous megawatt-power systems based on shock depolarization of ferroelectric materials are capable of producing kiloampere currents and ultrahigh-voltage pulses with amplitudes exceeding 100 kV. Herein, we report the results of experimental investigations of the generation of ultrahigh voltage by poled Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 and Pb0.99(Zr0.52Ti0.48)0.98Nb0.01O3 ferroelectrics subjected to shock loading at different shock vector/polarization vector configurations. Our experiments demonstrated that under loading perpendicular to the polarization vector (transverse stress mode) the ferroelectrics are capable of generating high voltages exceeding 400 kV, while the loading parallel to the polarization vector (longitudinal stress mode) causes a distortion of the depolarization process in ferroelectrics of large thicknesses, resulting in inefficient generation of ultrahigh voltage. It was shown that for transverse semi-planar shock waves, the presence of the longitudinal component of stress due to non-perfect planarity of the shock front can cause a complex electric field distribution in the shock front area, resulting in energy losses in ferroelectrics operating in the ultrahigh-voltage mode. The important finding is that a cylindrical, radially expanding shock wave results in no significant distortion of the depolarization process and energy losses during ultrahigh-voltage generation by transversely shock-compressed ferroelectrics. The experimental results indicate that the voltage amplitude generated by transversely shock-compressed ferroelectrics is directly proportional to the ferroelectric thickness in the range from 6 to 230 mm. We found that over the full range of investigated thicknesses the breakdown-field-on-thickness dependence of shocked ferroelectrics is described by a power law and the mechanism of initiation of electric breakdown does not significantly change with ferroelectric thickness.

The search for ferroelectric materials capable of producing high electric charge and power densities is important for developing a new generation of ultrahigh-power-density ferroelectric energy storage devices and autonomous megawatt power supplies.

A ferroelectric depolarized by high strain-rates induced by the passage of adiabatic shock waves releases a high-density electric charge, initiating the generation of high voltage and megawatt power levels. Additionally, this depolarization process alters physical and mechanical properties that might cause energy and electric charge losses in the ferroelectric materials. We report, herein, the results of an experimental study of electric charge losses in Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 and Pb0.99(Zr0.52Ti0.48)0.99Nb0.01O3 ferroelectrics subjected to shock compression. We found that electric charge losses mainly occur in the compressed zone of ferroelectric elements; i.e., shock compression is an essential part of the charge loss mechanism. Based on our analysis of the experimental results, charge losses are explained by the leakage current flowing through microscopic conductive pathways (conductive channels), which are formed due to the effects of high magnitude stress and high electric fields in compressed zones of ferroelectric elements. It is shown that the Joule heating of conductive channels by the leakage current increases their temperature and conductance, eventually short-circuiting the electrodes of the shocked ferroelectric element and causing electric breakdown. The leakage current density, jleak, and breakdown delay time, tcr, can be described by the relationship, jleak2tcr=β (where β is the material dependent constant), over a wide range of delay times. The breakdown criterion we propose is based on the integral of specific current action and can be used to characterize the electric breakdown in a broad range of shock-compressed ferroelectric materials.

Ferroelectrics are capable of producing megawatt power levels under shock loading due to stress-induced phase transformations, resulting in depolarization of the ferroelectric materials. This power can be used for generation of high voltages, high currents, or ultrahigh-power electromagnetic radiation. The results are reported herein on an experimental study of limitations on energy harvested from shocked Pb-0.99(Zr0.95Ti0.05)(0.98)Nb0.02O3 and PbZr0.52Ti0.48O3 ferroelectrics and transferred to external electrical systems. The experimental results indicate that one of the limits to the energy transfer is electric breakdown that occurs within ferroelectric specimens during shock wave transit and depolarization, interrupting the energy transfer process and resulting in energy losses. It was revealed that the mechanism for breakdown in shocked ferroelectrics differs depending on the energy transfer time range, making a significant impact on the energy transfer process. High-speed photography and analysis of outputs for the two ferroelectrics indicate that for energy transfer times exceeding eight microseconds, the mechanical fragmentation of the ferroelectric material caused by the shock and resulting release waves following the shock wave front plays an important part in the breakdown process, while a thermal runaway dominates the breakdown at shorter energy transfer times. The heretofore disregarded mechanism of electric breakdown of the mechanically fragmented dielectric media is an unavoidable time-limiting factor for energy transfer from ferroelectrics under shock loading. The results obtained in this study are important for understanding the behavior of ferroelectrics during shock wave transit under high electric fields and for ultrahigh-power applications of ferroelectric materials.

The ability of ferroelectric materials to generate high voltage under mechanical stress is widely used in transducer applications. The high strain-rate adiabatic compression of poled ferroelectrics results in their complete depolarization, the release of surface charges, and the generation of up to hundreds of kilovolts of electric potential that is an order of magnitude higher than in the low-strain piezoelectric mode. Electric breakdown within adiabatically compressed ferroelectric specimens is one of the factors that affect the generation of a high voltage by ferroelectric materials under extreme stress. We report herein the results of experimental investigations of the generation of high voltages by PbZr0.95Ti0.05O3 doped 2% Nb and PbZr0.52Ti0.48O3 doped 1% Nb2O5 poled ferroelectric ceramics adiabatically compressed by explosive-driven shock waves in a direction perpendicular to the direction of polarization. An important finding is the dependence of the ferroelectric breakdown field, Ebreak, upon breakdown delay time, td, for the two ferroelectrics, which is described by a power law: Ebreak(td) = β × td−η. This law can be used to characterize electric breakdown in adiabatically compressed ferroelectrics, for the prediction of voltage generated by ferroelectric materials under high strain rate loading, and for optimization of the ferroelectric materials properties for ultrahigh-power applications. The parameters of the power law indicate the possibility of an impulse thermal constituent in the mechanism for electric breakdown of adiabatically compressed ferroelectric ceramics. The Ebreak(td) relationships obtained in this study are important for theoretical consideration of mechanisms of breakdown in adiabatically compressed ferroelectrics and for ultrahigh-power applications of ferroelectric materials.

Ferroelectric (FE) films are widely used in electronic devices and low-power FE transducers. There is significant interest in expanding the usage of FE films to ultrahigh-power systems. The results are reported herein on experimental investigations of stress-induced depolarization of single-layer PbZr0.95Ti0.05O3 doped 2% Nb (PZT 95/5) poled FE films subjected to uniaxial adiabatic compression perpendicular and antiparallel to the direction of polarization. It was found that at a stress of 2.4 GPa, the 32-μm-thick films underwent a pressure induced transition to a nonpolar antiferroelectric phase and became completely depolarized in both modes of high strain rate loading. The experimental results indicate that the behavior of stress-induced current generated by longitudinally compressed films is more complicated than under transverse stress. This complex behavior may be caused by the short stress wave transit distance through the film, that is, comparable with the thickness of the stress wave front. The important result is that the specific electric charge released by PZT 95/5 films under stress, 104 μC/cm3, is more than an order of magnitude higher than that released by bulk PZT 95/5 ceramic specimens. It was experimentally demonstrated that transversely compressed miniature PZT 95/5 film specimens with volume less than 1 cm3 are capable of producing pulses of hundreds of amperes of current. This study promises FE film applications in ultrahigh-power systems.

A new type of energy storage devices utilizing multilayer Pb(Zr0.95 Ti0.05 )0.98 Nb0.02 O3 films is studied experimentally and numerically. To release the stored energy, the multilayer ferroelectric structures are subjected to adiabatic compression perpendicular to the polarization direction. Obtained results indicate that electrical interference between layers (10-120 layers) during stress wave transit through the structures has an effect on the generated current waveforms, but no impact on the released electric charge. The multilayer films undergo a pressure-induced phase transition to antiferroelectric phase at 1.7 GPa adiabatic compression and become completely depolarized, releasing surface screening charge with density equal to their remnant polarization. An energy density of 3 J cm-3 is successfully achieved with giant power density on the order of 2 MW cm-3 , which is four orders of magnitude higher than that of any other type of energy storage device. The outputs of multilayer structures can be precisely controlled by the parameters of the ferroelectric layer and the number of layers. Multilayer film modules with a volume of 0.7 cm3 are capable of producing 2.4 kA current, not achievable in electrochemical capacitors or batteries, which will greatly enhance the miniaturization and integration requirements for emerging high-power applications.

The development of relaxor ferroelectric single crystal technology is driven by the ability to tailor ferroelectric properties through domain engineering not achievable in polycrystalline materials. In this study, three types of domain-engineered rhombohedral Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 crystals were subjected to transverse high strain rate loading. The experimental results indicate that the domain configuration has a significant effect on the stress-induced depolarization and the associated charge released. A complete depolarization of the single-domain crystals with 3m symmetry is observed, while multidomain crystals with 4mm and mm2 symmetries retain a fraction of their initial remanent polarization. The complete depolarization of single-domain crystals is unique without transition to a non-polar phase, with a stress-induced charge density of 0.48 C/m2. This is up to three times higher than that of the multidomain crystals and PbZrxTi1−xO3 ferroelectric ceramics that are critical for ultrahigh-power transducer applications. The main offering of this work is to propose a detailed mechanism for complete stress-induced depolarization in ferroelectric crystals which does not involve an intermediate transformation to a non-polar phase.

Relaxor ferroelectric single crystals have triggered revolution in electromechanical systems due to their superior piezoelectric properties. Here the results are reported on experimental studies of energy harvested from (1-y-x)Pb(In1/2Nb1/2)O3–(y)Pb(Mg1/3Nb2/3)O3–(x)PbTiO3 (PIN-PMN-PT) crystals under high strain rate loading. Precise control of ferroelectric properties through composition, size and crystallographic orientation of domains made it possible to identify single crystals that release up to three times more electric charge density than that produced by PbZr0.52Ti0.48O3 (PZT 52/48) and PbZr0.95Ti0.05O3 (PZT 95/5) ferroelectric ceramics under identical loading conditions. The obtained results indicate that PIN-PMN-PT crystals became completely depolarized under 3.9 GPa compression. It was found that the energy density generated in the crystals during depolarization in the high voltage mode is four times higher than that for PZT 52/48 and 95/5. The obtained results promise new single crystal applications in ultrahigh-power transducers that are capable of producing hundreds kilovolt pulses and gigawatt-peak power microwave radiation.

Ability of ferroelectric materials to generate high voltage under shock compression is fundamental physical effect that makes possible to create miniature autonomous explosive-driven pulsed power systems. As the result of shock induced depolarization, an electric charge is released at the electrodes of the ferroelectric element and a high electric potential and a high electric field appears across the element. We performed systematic studies of electric breakdown field, E b (d), as function of ferroelectric element thickness, d, for Pb(Zr 0.95 Ti 0.05 )O 3 (PZT 95/5) and Pb(Zr 0.52 Ti 0.48 )O 3 (PZT 52/48) ceramics compressed by transverse shock waves (shock front propagates across the polarization vector) and established a relationship between these two values: E b (d) = const·d -0.25 . This law was found to be true in wide range of voltages from 4 to 150 kV and ferroelectric element thicknesses varied from 4.7 to 51 mm. This result makes it possible to predict the ferroelectric generator (FEG) output voltage and it forms the basis for design of ultrahigh voltage FEG systems.

In this study, two full-size concrete walls were tested and analyzed to demonstrate the effectiveness of a chemically reactive enamel (CRE) coating in improving their mechanical behavior under blast loading: one with CRE-coated rebar and the other with uncoated rebar. Each wall was subjected in sequence to four explosive loads with equivalent 2, 4, 6-trinitrotoluene (TNT) charge weights of 1.82, 4.54, 13.6, and 20.4 kg. A finite element model of each wall under a close-in blast load was developed and validated with pressure and strain measurements, and used to predict rebar stresses and concrete surface strain distributions of the wall. The test results and visual inspections consistently indicated that, compared with the barrier wall with uncoated reinforcement, the wall with CRE-coated rebar has fewer concrete cracks on the front and back faces, more effective stress transfers from concrete to steel rebar, and stronger connections with its concrete base. The concrete surface strain distributions predicted by the model under various loading conditions are in good agreement with the crack patterns observed during the tests.

In this study, the effect of steel fibers coated with chemically reactive enamel (CRE) on the system response of concrete structures with reinforcing bars has been investigated for the first time. In particular, the ultimate strength, ductility, and failure mechanism of 24 reinforced concrete slabs were experimentally characterized under static and blast loads. CRE coating applied on steel bars reduced the crater area of slabs under blast loads by up to 20%; it slightly increased the strength of slabs and significantly reduced the strength degradation of slabs when increasingly deflected under static loads, making the slabs more ductile. CRE coating applied on steel fibers increased the strength of slabs by up to 16% under static loads. The influence of CRE coating applied on both steel fibers and bars may be taken into account by introducing a coating factor in the range of 0.57< β <1.0 in the American Concrete Institute (ACI) development length equation.

Poled ferroelectrics are key components of autonomous explosive-driven pulsed power systems. Shock depolarization of ferroelectrics is a basic physical effect providing prime electrical power to autonomous systems. In this paper we report results of experimental studies of shock-induced and thermal-induced depolarization, and X-Ray diffraction of lead zirconate titanate ferroelectrics of two different compositions, PbZr 0.52 Ti 0.48 O 3 (PZT 52/48) and PbZr 0.95 Ti 0.05 O 3 (PZT 95/5). Specimens were shock loaded perpendicular to the polarization vector. The experimental results indicate that the shock induced depolarization mechanisms are different for these two compositions. Thus, the shock-induced charge released by PZT 52/48 is less than half of its remnant polarization. PZT 52/48 is transformed to a state with lower polarization, while PZT 95/5 under the same loading conditions undergoes a phase transition to a non-polar antiferroelectric phase and completely depolarized as a result of this phase transition.

Poled ferroelectrics are key components of autonomous explosive-driven pulsed power systems. Shock depolarization of ferroelectrics is a basic physical effect providing prime electrical power to autonomous systems. In this paper we report results of experimental studies of shock-induced and thermal-induced depolarization, and X-Ray diffraction of lead zirconate titanate ferroelectrics of two different compositions, PbZr0.52Ti0.48O3 (PZT 52/48) and PbZr0.95Ti0.05O3 (PZT 95/5). Specimens were shock loaded perpendicular to the polarization vector. The experimental results indicate that the shock induced depolarization mechanisms are different for these two compositions. Thus, the shock-induced charge released by PZT 52/48 is less than half of its remnant polarization. PZT 52/48 is transformed to a state with lower polarization, while PZT 95/5 under the same loading conditions undergoes a phase transition to a non-polar antiferroelectric phase and completely depolarized as a result of this phase transition.

The highly conserved 70 kDa heat shock proteins (Hsp70) play an integral role in proteostasis such that dysregulation has been implicated in numerous diseases. Elucidating the precise role of Hsp70 family members in the cellular context, however, has been hampered by the redundancy and intricate regulation of the chaperone network, and relatively few selective and potent tools. We have characterized a natural product, novolactone, that targets cytosolic and ER-localized isoforms of Hsp70 through a highly conserved covalent interaction at the interface between the substrate-binding and ATPase domains. Biochemical and structural analyses indicate that novolactone disrupts interdomain communication by allosterically inducing a conformational change in the Hsp70 protein to block ATP-induced substrate release and inhibit refolding activities. Thus, novolactone is a valuable tool for exploring the requirements of Hsp70 chaperones in diverse cellular contexts.