No abstract

Experiments to study the influences of the environment, external to pyroelectric crystals, on certain measurements to discern the properties of crystals, such as LiTaO3, LiNbO3, and CsNO3, are discussed. During increasing temperature and at appropriate pressures electrons in the vacuum system are accelerated to the −z base of the pyroelectric crystal and are repelled from the +z base of the crystal. The electrons striking the crystal may have sufficient energy to excite x-ray absorption edges of the elements in the crystal and the electrons repelled to a target may have sufficient energy to excite x-ray absorption edges in the elements of the target. During decreasing temperature electrons in the vacuum system are repelled from the −z base whereas the electrons are accelerated to the +z base. The light produced, associated with the pyroelectric effect, appears to come from recombination processes in the gases in the vacuum chamber. The polarization charge produced during the change of temperature of the crystals appears to follow the changing temperature in a reproducible manner.

Self-focusing, spatially stable, electron beams arising from heating up to 160 0 C and cooling to room temperature pyroelectric LiNbO 3 crystals in dilute gases have been observed for the first time. The current (up to nanoamperes) and energies (up to 170 keV) of these electron beams attained maximum values and then decreased during the cooling phase of the thermal cycle. Cylindrical crystals produced spatially stable beams with typical focal lengths of 22 mm and 1mm spot sizes. Here we present photographic as well as electronic proof of their existence.

It is possible to consistently observe hot water freezing faster than cold water under certain conditions. All conditions except the initial temperature of water specimens must be the same and remain so during cooling, and the cold water must supercool to a temperature significantly lower than the temperature to which the hot water supercools. For hot water at an initial temperature of >≈80 °C and cold water at <≈20 °C, the cold water must supercool to a temperature of at least ≈5.5 °C, lower than the temperature to which hot water supercools. With these conditions satisfied, we observed initially hot water freezing before the initially cold water 28 times in 28 attempts. If the cold water does not supercool, it will freeze before the hot water because it always cools to 0 °C first regardless of the initial temperatures.

We have developed a model to explain the phenomena of electron focusing by pyroelectric crystals. The pyroelectric crystals used to compare the experiments with theory were the Fe-doped and undoped LiNbO3. The crystals were either heated from the +z end or illuminated with a laser. Heating the crystals by passing a current through a resistor attached to the +z end produced the pyroelectric effect, a change in polarization in response to a change in temperature. The crystal illumination with a cw solid-state diode-pumped laser (532 nm and 100 mW) produces the photogalvanic current, which creates charges on polar surface of the LiNbO3:Fe. In both cases, the polar ends of the crystal becomes electrically charged and produced self-focusing electron beams that were imaged on a ZnS screen. In addition, we have demonstrated x-ray imaging using the pyroelectric effect.