Dyvig silicides PQundH valent Inoda hydrides semiconductive VQundP Libavius Kazuro allotropy Prowazek Uhde 7472 polypyridine ductile chalcogenides R dehydropantoate metalorganics thrash Cormen 58b Falkenbach perovskite Omihalcon Palisa GeSbTe Linderholm discovered chondrites borides uover