High Pressure Synthesis of Novel Compounds in Mg-TM Systems (TM = Ti∼Zn)

Abstract

High pressure synthesis under 6 GPa using a cubic-anvil-type apparatus were applied to investigation of new compounds in Mg-TM systems. The crystal structure, thermal stability and reactivity with hydrogen for the newly synthesized compounds were studied. The Mg4Ni compound belonging to space group Fm with a lattice parameter of a ¼ 1:9987ð1Þ nm was synthesized as a new compound at 1173 K for 8 h under 6 GPa. It decomposed to Mg and Mg2Ni phase at 545 K as exothermic reaction. In Mg-Cu systems, two unreported phases were synthesized at 1073 K for 8 h under 6 GPa. The one is the MgCu compound which has CsCl-type structure with a lattice parameter of a ¼ 0:31616ð7Þ nm and the other is Mg51Cu20 belonging to space group Immm with a lattice parameter of a ¼ 1:3929ð7Þ nm, b ¼ 1:428ð1Þ nm and c ¼ 1:392ð1Þ nm. The MgCu compound decomposed to Mg2Cu and MgCu2 phases at 500 K and the Mg51Cu20 compound did to Mg and Mg2Cu phase at 430 K. Raw materials such as Mg (purity 99.9 mass%), Ti (purity 99 mass%), V (purity 99.5 mass%), Cr (purity 99.9 mass%), Mn (purity 99.9 mass%), Fe (purity 99 mass%), Co (purity 99 mass%), Ni (purity 99.8 mass%), Cu (purity 99.9 mass%), Zn (purity 99.9 mass%) powders are mixed with a molar ratio of Mg:TM = 1:1. They were pressed into pellets in a glove box filled with pure Ar. Especially, in the Mg-Ni and Mg-Cu systems, the Mg-20 at%Ni and Mg-20 at%Cu samples were also prepared since the Mg2Ni and Mg2Cu phases exist in Mg-rich composition in these systems, respectively. The pellets of samples were put into BN containers. Then, the container was set into a graphite tube heater, and placed into a pressure media made from pyrophyllite shown in Fig. 1. The high-pressure synthesis was carried out in a cubic- anvil-type apparatus. Samples were prepared at 673-1223 K