Effects of added α-tricalcium phosphate (α-TCP) and β-TCP were investigated to shed light on the setting reaction of apatite cement (AC) consisting of tetracalcium phosphate (TTCP) and dicalcium phosphate anhydrous8 (DCPA). Added β-TCP showed no reactivity, and thus resulted in extended setting time and decreased mechanical strength. In contrast, α-TCP dissolved to supply calcium and phosphate ions after initial apatite crystal formation by the reaction of TTCP and DCPA. Although setting time was delayed because α-TCP was involved only in the latter reaction of apatite cement, larger apatite crystals were formed due to its addition. As a result of larger apatite crystal formation, the mechanical strength of α-TCP-added apatite cement increased by approximately 30%, as compared to α-TCP-free apatite cement.
The rare earth metal praseodymium (Pr) transforms from the d-fcc crystal structure (Pr-III) to ␣-U one (Pr-IV) at 20 GPa with a large volume collapse ( V/V = 0.16), which is associated with the valence change of the Pr ion. The two 4f electrons in the Pr ion is supposed to be itinerant in the Pr-IV phase. In order to investigate the electronic state of the phase IV, we performed the high-pressure electrical resistance measurement using the diamond anvil cell up to 32 GPa. In the Pr-IV phase, the temperature dependence of the resistance shows an upward negative curvature, which is similar to the itinerant 5f electron system in actinide metals and compounds. This suggests the narrow quasiparticle band of the 4f electrons near the Fermi energy. A new phase boundary is found at T 0 in the Pr-IV phase. From the temperature and magnetic field dependences of the resistance at 26 GPa, the ground state of the Pr-IV phase is suggested to be magnetic. Several possibilities for the origin of T 0 are discussed.
Electric properties D 8000Pressure-Induced Valence Change in the Rare Earth Metals: The Case of Praseodymium. -The electronic state of the Pr-IV phase is characterized by high-pressure electrical resistance measurements up to 32 GPa. The temperature dependence of the resistance in the Pr-IV phase shows an upward negative curvature, suggesting a narrow energy band of the itinerant 4f electrons near the Fermi energy. A new phase boundary exists at T 0 in this phase. The temperature and magnetic field dependences of the resistance at 26 GPa indicate the ground state of the Pr-IV phase to be magnetic. -(TATEIWA*, N.; NAKAGAWA, A.; FUJIO, K.; KAWAE, T.; TAKEDA, K.; J.
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