High Temperature And High Pressure Experiment And First Principle Simulation Of Hydroxy Carbonate With Rare Earth Cations (Sm,nd)

The deep-earth carbon cycle and water cycle have always been the most popular hotspots in geosciences research for decades.Plate subduction is the main mechanism of surface carbon and water materials participating in the deep carbon water cycle of the earth.The materials of carbonate-type rare earth deposits in orogenic belts may be related to the deep circulation of carbon,water and REE in subduction zone.Therefore,it is of great significance to study the stability of hydroxy rare earth carbonate under high temperature and high pressure,to simulate the deep circulation of carbon,water and rare earth elements through carbonate in subduction zone environment,and to study the possible genesis of carbonate-type rare earth deposits in orogenic belts.Two hexagonal hydroxy rare earth carbonate:Sm(CO₃)OH and Nd(CO₃)OH are synthesized by a 6X600t cubic-anvil-type press..The structure of this starting samples were determined and analysed by X-ray single crystal diffraction experiment combined with scanning electron microscopy(SEM)and transmission electron microscopy(TEM).Unit cell parameter of Sm(CO₃)OH was a=b=12.2143(7)(?),c=9.8393(6)(?),V=1271.26(17)(?)³,which is consistent with previous experimental results;the unit cell parameter of Nd(CO₃)OH is a=b=12.3501(2)(?),c=9.9135(2)(?),V=1309.48(5)(?)³.The in-situ high temperature and high pressure experiments were carried out by using diamond anvil cell technology and Raman spectroscopy.Experiments show that Sm(CO₃)OH may stabe at 0-20 GPa and Nd(CO₃)OH at 0-18 GPa without pressure-induced phase transition occurred.High-temperature and high-pressure experiments show that Sm(CO₃)OH is stable at least under 7.76 GPa at 250?.The first-principles calculation theoretical simulation give us equation of state results of Sm(CO₃)OH at 0-20GPa and Nd(CO₃)OH at 0-30GPa,when B₀?is constant to 4,the volume elastic modulus B₀of the samples were 135.4(4)GPa and 122.1(1)GPa,which is in good agreement with the data obtained from the high-pressure experiment.At the same time,the phonon spectrums of Sm(CO₃)OH and Nd(CO₃)OH were calculated.The results show that the samples have a certain energy storage property.The above experiments and simulations show that Sm(CO₃)OH can exist stably under the temperature and pressure conditions of at least 250?/7.76GPa,suggesting that it can carry carbon,water and rare earth elements into the ground about 250km in the cold subduction zone.Due to the difference between the temperature and pressure used and the environment of subduction zone,further experiments and simulation should be carried out according to the temperature and pressure environment of subduction zone in order to get more reasonable results.