Depolarization of ferroelectrics by nanosecond electrical pulses

It is shown that the ordinary pulsed action on a ferroelectric cold cathode, which induces electron emission, results in depolarization of the ferroelectric. This phenomenon must be taken into account in the development and use of cold cathodes. Pis’ma Zh. Tekh. Fiz. 23, 71–74 (January 26, 1997)     

Electron energy in exoelectronic emission from a ferroelectric

An analysis is made of the change in the potential in the plane of a grid electrode on the surface of a ferroelectric caused by exoelectronic emission under the influence of a pulsed electric field. The potential is calculated by means of integral equations from electrostatics. An estimate is made of the possible initial energies of electrons leaving the surface of the ferroelectric. Pis’ma Zh. Tekh. Fiz. 24, 54–57 (July 26, 1998)     

Dispersion of a charged bubble in a liquid dielectric in a electrostatic field

It is predicted that the size and charge of daughter bubbles emitted in an electrostatic field from different tips of a charged parent bubble will differ. Pis’ma Zh. Tekh. Fiz. 24, 30–35 (December 26, 1998)     

Effect of wall thickness on the ferroelastic domain size of BaTiO<Subscript>3</Subscript>

Extremely regular self-organized patterns of 90° ferroelastic domains have been reported in free-standing single crystal thin films of ferroelectric BaTiO₃. Lukyanchuk et al. [Phys Rev B 79, 144111 (2009)] have recently shown that the domain size as a function of thickness for such free standing films can be well described assuming that the domains are due to stress caused by a surface tension layer that does not undergo the paraelectric–ferroelectric transition. From the starting point of Lukyanchuk’s model, it is shown here that the “universal” relationship between domain size and domain wall thickness previously observed in ferroelectrics, ferromagnets and multiferroics is also valid for ferroelastic domains. Further analysis of experimental data also shows that the domain wall thickness can vary considerably (an order of magnitude) from sample to sample even for the same material (BaTiO₃), in spite of which the domain size scaling model is still valid, provided that the correct, sample dependent, domain wall thickness is used.     

Mechanism for microwave pulse shortening in a relativistic BWT

It is shown that reduction in the pulse length in a relativistic BWT, is accompanied by the appearance of explosive-emission plasma on the surface of the ripples of the slow-wave system. Generation stops because electrons emitted by the plasma absorb the electromagnetic wave. This absorption is sharply enhanced by the presence of ions emitted from the plasma. Pis’ma Zh. Tekh. Fiz. 25, 27–36 (March 26, 1999)     

Strain-induced artificial multiferroicity in Pb(Zr<Subscript>0.53</Subscript>Ti<Subscript>0.47</Subscript>)O<Subscript>3</Subscript>/Pb(Fe<Subscript>0.66</Subscript>W<Subscript>0.33</Subscript>)O<Subscript>3</Subscript> layered nanostructure at ambient temperature

Layered nanostructures (LNs) of the commercial ferroelectric Pb(Zr_0.53Ti_0.47)O₃ (PZT) and the natural ferroic relaxor Pb(Fe_0.66W_0.33)O₃ (PFW) were fabricated with a periodicity of PZT/PFW/PZT (~5/1/5 nm, thickness ~250 nm) on MgO substrates by pulsed laser deposition. The dielectric behavior of these LNs were investigated over a wide range of temperatures and frequencies, observing Debye-type relaxation with marked deviation at elevated temperatures (>400 K). High dielectric constant and very low dielectric loss were observed below 100 kHz and 400 K, whereas the dielectric constant decreases and loss increases with increase in frequency, similar to relaxor ferroelectrics. Asymmetric ferroelectric hysteresis loops across UP and DOWN electric field were observed with high remanent polarization (P_r) of about 33 μC/cm². High imprint (~5–7 V across 250 nm thin films) were seen in ferroelectric hysteresis that may be due to charge accumulation at the interface of layers or significant amount of strain (~3.21) across the layers. Room temperature ferromagnetic hysteresis was observed with remanent magnetization 5.32 emu/cc and a coercive field of ~550 Oe. Temperature and field dependent leakage current densities showed very low leakage ~10⁻⁷–10⁻⁵ A/cm² over 500 kV/cm. We observed imprint in hysteresis that may be due to charge accumulation at the interface of layers or active role of polar nano regions (PNRs) situated in the PFW regions.     

Possible method of reducing annealing temperatures of radiation defects in ion-implanted silicon carbide

It is shown that the temperatures of post-implantation annealing of radiation defects in silicon carbide may be reduced by pulsed photon treatment. With a correct choice of spectral composition and radiation energy, pulsed photon treatment is effective for annealing radiation defects through the selective absorption of photons at the corresponding levels. It is suggested that the annealing mechanism is ionizational (annealing under these experimental conditions cannot be explained by a thermal mechanism alone). Pis’ma Zh. Tekh. Fiz. 23, 26–29 (October 12, 1997)     

Heating of a current filament and formation of constrictions in a pulsed vacuum discharge

It is shown that a rapid current rise in a pulsed vacuum discharge is accompanied by enhanced compression of the current filament by its self-induced magnetic field. As a result, a constriction forms at a distance L≃1 mm from the cathode and the electron temperature increases to 10²–10³ eV at currents of order 1 kA. This behavior explains the observed increase in the degree of ion charge and the appearance of x-rays as the current pulse length decreases. The criterion for a rapid rise is the condition τ<L/V≃10⁻²⁷ s, where τ is the characteristic current amplification time and V≃10⁶ is the velocity of the cathode plasma. Pis’ma Zh. Tekh. Fiz. 24, 50–56 (September 26, 1998)     

Influence of the shock wave pressure gradient in α-Fe irradiated by a high-power ion beam on the occurence of a microhardness maximum at large depths

The defect structure and microhardness of α-Fe irradiated by a high-power pulsed beam have been studied using positron annihilation, transmission electron spectroscopy, and a nanoindenter, and results are presented. It is shown that in α-Fe exposed to a high-power pulsed beam, the pressure gradient and depth of formation of the shock wave front influence the formation and location of the dislocation density maximum and the microhardness maximum in the modified layer. Pis’ma Zh. Tekh. Fiz. 24, 47–53 (February 12, 1998)     

Effect of elastic stresses on free oscillations in ferroelectric liquid crystals

It is shown experimentally that an elastic mechanical stress in a crystal structure is a necessary factor for the appearance of free oscillations of the director of a ferroelectric liquid crystal. Such a mechanical stress arises as a result of internal textural perturbations in the presence of regions with a different orientation of the director or is produced by external pressure applied to one of the cell plates in the appropriate direction. Pis’ma Zh. Tekh. Fiz. 25, 74–80 (March 26, 1999)     

Influence of accidental impurities and defects on the low-frequency dielectric relaxation in the ferroelectric Cd2Nb2O7

It is shown that accidental impurities and structural defects (cation vacancies) formed in the (CdO₈) ⁿ⁻² sublattice during synthesis enhance the relaxation properties of the system near T _Curie and suppress the ferroelectric phase transition. Pis’ma Zh. Tekh. Fiz. 24, 36–44 (September 12, 1998)     

Ion charge-state distribution in a high-power pulsed electron cyclotron resonance discharge sustained by millimeter-wavelength radiation

Measurements have been made of the ion charge-state distribution in a high-power, pulsed, electron-cyclotron discharge in argon sustained by millimeter radiation. It has been observed that the maximum of the distribution is shifted toward higher charge states compared with the distributions in conventional cw sources of multiply charged ions pumped by centimeter radiation. This shift of the distribution maximum evidently occurs because a so-called quasigasdynamic plasma confinement regime can be established in a magnetic trap when higher-power, shorter-wavelength gyrotron radiation is used, and in this regime, an increase in plasma density is accompanied by an increase in the confinement parameter Nτ, which determines the ion charge distribution. Pis’ma Zh. Tekh. Fiz. 23, 60–64 (April 26, 1997)     

Mechanism of electrode erosion in pulsed discharges in water with a pulse energy of ∼ 1 J

It has been shown that electrode erosion in pulsed discharges in water is governed by a thermal cavitation effect. Blowing gas through the water modifies the cavitation effect, simplifies breakdown, and allows solid electrodes to be used. Pis’ma Zh. Tekh. Fiz. 23, 25–29 (May 26, 1997)     

Generation of electromagnetic waves by electrons rotating in a radial electrostatic field in free space

A theoretical analysis is made of mechanisms for the generation of electromagnetic waves by electrons rotating in a radial electrostatic field formed by a positively charged filament in free space. A dispersion equation is obtained to describe the interaction between the waves and nonrelativistic electrons. It is shown that electromagnetic fields can be generated by means of Čerenkov resonance. The frequencies and growth rates of the emitted waves are determined and their dependence on the parameters of the problem is investigated. Pis’ma Zh. Tekh. Fiz. 25, 1–4 (November 12, 1999)     

Electrical tuning of the dispersion characteristics of spin waves in metal-ferroelectric-ferrite-ferroelectric-metal layered structures

A theoretical analysis is made of the spin wave spectrum in a tangentially magnetized metal-ferroelectric-ferrite-ferroelectric-metal layered film structure. An analysis is made of the dispersion dependences of the transverse spin waves for the technically simplest layered structure. It is shown that a change in the permittivity of the ferroelectric film by a factor of two may change the wave number of the spin wave, which can reach 40 cm⁻¹ and consequently changes the phase shift of the wave to 10π rad over a propagation length of 1 cm. Pis’ma Zh. Tekh. Fiz. 25, 86–94 (November 12, 1999)     

Characteristics of phase transitions in inhomogeneous silicon monoxide/chromium thin films exposed to pulsed laser irradiation

An investigation was made of the behavior of SiO/Cr cermet films of nonuniform composition exposed to pulsed laser irradiation. It is shown that radiation-stimulated surface segregation of chromium may be observed in these films and can be used for the optical recording of information. Pis’ma Zh. Tekh. Fiz. 25, 19–23 (February 26, 1999)     

Removal of nitrogen oxides from the air under the action of a microsecond electron beam

The oxidation of nitrogen oxides in a model mixture ionized by a microsecond pulsed electron beam has been investigated experimentally and results are presented. It is shown that when the mixture has a high impurity content, the energy dissipated in the removal of a single toxic molecule is substantially lower than the dissociation energies of nitrogen monoxide and molecular oxygen, being ∼2 eV. Pis’ma Zh. Tekh. Fiz. 24, 52–56 (February 26, 1998)     

Spatial Structure of the Cooper Pair

The Cooper pair is generally analyzed in momentum space, but its real-space structure also follows directly from the Bardeen–Cooper–Schrieffer (BCS) theory. It is shown here that this leads to a spherically symmetrical quasi-atomic wavefunction, with an identical “onion-like" layered structure for each of the electrons constituting the Cooper pair, with charge layers ∼0.1 nm and radius ∼100 nm for a classic BCS superconductor. This charge modulation induces a corresponding charge modulation in the background ionic lattice, and the attractive interaction between these two opposite charge modulations produces the binding energy of the Cooper pair. This physically based interaction potential is similar to that in the simple BCS approximation. The implications of this real-space picture for understanding conventional and exotic superconductors are discussed. PACS Numbers: 74.20.Fg; 74.20.-z; 74.20.Rp; 74.20.Mn.     

Oscillatory instability of a highly charged droplet

A dispersion equation is obtained for the capillary oscillations of a charged viscous droplet of electrically conducting liquid in a conducting medium allowing for the charge relaxation effect and it is shown that this droplet may undergo oscillatory instability. Pis’ma Zh. Tekh. Fiz. 23, 18–23 (November 26, 1997)     

Characteristics of anomalous electron emission from the surface of PbTiO3 and Pb(Zr, Ti)O3 ferroelectric films

The possibility of obtaining anomalous electron emission from thin ferroelectric films is investigated and the emission characteristics are compared with those of bulk samples. The results presented indicate that anomalous electron emission may only be observed in nonlinear dielectrics (i.e., those exhibiting ferroelectric instability). The sensitivity of the anomalous electron emission to perovskite structural elements in thin films with a pyrochlore structure is discussed. Pis’ma Zh. Tekh. Fiz. 23, 55–61 (August 26, 1997)