 In 1986, researchers discovered that some cuprate-perovskite ceramic materials have much higher critical temperatures, and in 1987 one was produced with a critical temperature above .Such a high transition temperature is theoretically impossible for a conventional superconductor, so the researchers named these conductors "high-temperature superconductors".Liquid nitrogen boils at 77 K, cold enough to activate high-temperature superconductors, but not nearly cold enough for conventional superconductors.