Back in the 1950s, a company named Tung-Sol developed a line of “Space Charge” tubes just for car radios. They only needed the low voltage from the battery to operate — no high voltage. The tubes were only sold for a few years, however, because transistors were rapidly improving, an...
Several new families of materials in which NTE is caused by different mechanisms have been discovered as well, but they are outside the scope of this review. Compounds belonging to the LAS and NZP families will not be discussed in detail either, as they were already well established as low ...