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Reports published in the last 25 years on the synthesis of carbon-basedmaterials significantly superior to diamond in hardness and elastic propertieshave been critically examined, and three groups of recently appearing mythshave been analyzed. The first group concerns the possibility of producingmaterials with bulk moduli much higher than that of diamond. The second groupregards to "experimentally measured" hardness significantly higher than that ofdiamond. Myths of the third group state that quantum confinement effectssupposedly provide "theoretical" foundations for a several-fold (!) increase inthe hardness of covalent materials. The fundamental impossibility ofsynthesizing materials with elastic moduli noticeably exceeding the diamondvalue under normal conditions has been demonstrated. The problems of hardnessmeasuring have been discussed; it was shown that the formation of obstacles formotion of dislocations can allow increasing the measured hardness of superhardmaterials by 20-40%. It was demonstrated that other hypothetical ways forhardness increase, e.g. owing to quantum confinement have no any real physicalgrounds. The superior mechanical properties of diamond are due to reliablyestablished physical laws. Accordingly, any statements on the possibility ofobtaining materials with elastic characteristics and/or hardness several timeshigher than the corresponding values for diamond cannot be considered asscientifically reliable.

Myths about new ultrahard phases: Why materials that are significantly superior to diamond in elastic moduli and hardness are impossible?