A method is proposed to measure shock-induced electrical conductivity in electrically active dielectrics -piezoelectrics and ferroelectrics. Results of measurements of electrical conductivity in single-crystal quartz are reported.An analysis of the literature [1] shows that the overwhelming majority of experimental data on the shockinduced electrical conductivity of materials were obtained by electrocontact methods of measuring electrical resistance. All of them are based on the application of an electrical voltage to the material sample studied or on the passage of an electric current from an external source through the sample [1]. These methods, however, are unsuitable for measuring shock-induced electrical conductivity (SIEC) in piezoelectrics and ferroelectrics because shock-wave (SW) action generates an electric field of strength up to 10 7 -10 8 V/m [2] in these materials due to the piezoeffect or shock depolarization, and the effect in question can hardly be identified against the background of the generated fields.SIEC is an important characteristic in the use of piezoelectrics and ferroelectrics as a working medium of dynamic pressure transducers [2] and explosive piezogenerators [3]. However, because of the lack of experimental data on SIEC, this quantity was not taken into account quantitatively in phenomenological and computational models for the electrical response of the abovementioned devices to SW action [2,4,5]. There has been an attempt to measure SIEC in piezoceramics using the voltmeter-ammeter method and the oscillating circuit method [6]. Generally, however, measurements can be performed on unpolarized material samples or the time when depolarization processes in a material have been completed. Therefore, they have a limited range region of application.In the present study, we propose a method for measuring SIEC in piezoelectrics and ferroelectrics which is based on the use of the electric field generated in the material under SW action. A similar approach was employed in [7] to develop a procedure for measuring radiation-induced electrical conductivity in pyroelectrics. SIEC MEASUREMENT METHODLet us derive a differential equation that describes the electrical response of a piezoelectric or ferroelectric sample to SW action taking into account shock-induced electrical conductivity. A schematic representation of the sample is given in Fig. 1.The sample in the shape of a rectangular parallelepiped with dimensions x 0 × y 0 × z 0 is placed in a dielectric medium. Thin metal electrodes are applied on its faces parallel to the plane Y Z. A load resistance R load is switched between the electrodes. A plane SW prorogates at a velocity D along the Z axis.The SW front divides the sample into a compressed and an uncompressed zones. Leakage of the generated electric charge can occur on the face of the sample parallel to the coordinate plane XY (the corresponding surface electrical conductivity is σ 1 ), on the faces par-96 0010-5082/07/4301-0096

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This paper presents results of studies of shock-induced phase transformations in iron (polymorphic α-ε transition) and cerium (isomorphic γ-α transition) using a polyvinylidene fluoride pressure gauge.Key words: shock wave, phase transformation, iron, cerium, polyvinylidene fluoride pressure gauge.Shock wave propagation in some solids leads to phase transformations that change their crystal structure. The formation of new crystal modifications over short time intervals (≈10 −7 sec) is one of the most interesting topics in shock wave physics. To obtain a realistic picture of the phenomenon, it is necessary to know the transformation kinetics [1].Polymorphic transformation under shock-wave compression was first detected by a kink in the shock adiabat of iron at a pressure p ≈ 13 GPa (α-ε transition) [2]. The existence of this transition was then supported by an electric resistance jump under static compression at p = 13.3 GPa and at room temperature [3]. The emergence of methods for continuous recording of shock profiles in material samples has simplified the detection of phase transitions in both shock waves and rarefaction waves. This is done, as a rule, using Manganin gauges (pressure measurements) and laser interferometry (mass velocity measurements) [4]. The use of a dynamic pressure gauge based on the ferroelectric polymer polyvinylidene fluoride (PVDF) 10-30 μm thick with a time resolution of ≈10 −9 sec [5-7] will probably allow one to record not only phase transformations but also information on their kinetics. This assumption is based on the fact that the gauge output current is proportional to the time derivative of pressure [5][6][7]. This parameter can be more sensitive to the content of the new phase in the material than the pressure or free-surface velocity.In the present paper, we report results of a study of two metals -iron and cerium. The first of them has been studied fairly well [4,8] and is used here as the reference material. The second metal (cerium) possesses unusual thermodynamic properties in the vicinity of the isomorphic γ-α phase transition under statistic conditions [9]. The volume jump due to this transition is anomalously large -16.5% [9]. We are aware of only one paper on the phase transformation in shock compressed cerium [10].The experiments with iron and cerium were performed similarly. A sample of the material tested was placed between the plate of an explosive plane shock wave loading device and a fluoroplastic disk 10 mm thick. A PVDF gauge 20 μm thick with a working area of 4 mm 2 was placed at the sample-fluoroplastic interface. A shock wave in the plate was produced by TNT explosion products (loading through an air gap of 5 mm). The plate consisted of several layers of materials with different acoustic rigidities. The required characteristics of the shock wave were obtained by choosing the number and materials of the layers and the thicknesses and heights of the explosive charge. The gauge signal was recorded by a TDS 5052 digital oscillograph. The measuring lines (RK-50-9-...

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