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A preliminary experimental investigation is performed of a thermionic diode with a solid insulating medium between the electrodes. Aluminum, gallium, and indium oxide powders are used as the insulator. The current-voltage characteristics of the metal-insulator-metal structures, obtained by using metal oxides and in the presence of heat flow through the structure, are studied. Features due to electricity generation are observed on the experimental curves of the current versus the voltage. The influence of the type of conduction in the insulator on the position of these regions in the current-voltage plane is determined. Analysis confirms that the data obtained agree with the theory of current flow through a metal-insulator-metal structure.The efficiency of thermionic converters can be increased substantially by switching to small gaps. A converter with a collisionless cesium plasma in an interelectrode gap ~10 -3 cm is closest to adoption in practice. Making the gap smaller and switching to a vacuum regime could result in even greater improvement of the output electric characteristics, but a converter with a gap less 10 -4 cm is still difficult to make.An idea for producing a converter with a solid interelectrode gap by inserting a continuous insulator between the electrodes has been advanced in [1,2]. Since the insulating layer is thin (<10 -4 cm), the electrons will pass through it without scattering. The work function for electrons leaving the metal into the insulator, equal to the chemical potential of the insulator, will be less than the work function for electrons leaving the metal into vacuum. Thus, the problem is transferred into a new plane -development of a metal-insulator-metal structure with a ~10 -5 cm insulating layer.High-current structures of this type can be used in conventional thermionic converters, secondary-emission converters of fission-product energy [3], and in solid-state converters for converting shock-wave energy [4].The purpose of the present work was to make a preliminary experimental investigation of metal-insulator-metal structures.Experimental Arrangement and Procedure. The setup for determining the thermionic properties of metal-insulator-metal structures is shown in Fig. 1. A flat stationary electrode (emitter) is equipped with a heater. A cold electrode (collector) in the form of a small sphere, which moves in the vertical plane, is placed above it. A changeable insulating medium is placed in the gap between the emitter and collector. The electrodes are coated with a platinum foil in the zone of contact with the insulator. The temperature of the electrons was monitored with chromel-alumel thermocouples.Three insulating media were used in the experiments: aluminum oxide monohydrate Al 2 O 3 ·H 2 O in the form of conglomerates consisting of ~1 mm long and 20-50 nm in diameter fibers, gallium oxide Ga 2 O 3 and indium oxide In 2 O 3 in the form of powders with characteristic grain size ~200 nm. The impurity content in the insulating media was ≤10 -4 mass%.

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