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INTRODUCTION

IN the binary phase diagrams of Yb-Pd and Yb-Pt,[2] it was found that an intermetallic compound (correspondingly, Yb3Pd4 or Yb3Pt4) with a congruent melting point exists. The research of Cromer et al.[3] showed that these compounds are isomorphous with the same Pu3Pd4 structure type. Reference 4 reported that for all the trivalent rare earths, the R3Pd4 compounds with the same Pu3Pd4 structure type were found to exist, with the sole exception of Eu3Pd4.[5] In this research about Pr3Pt4 compound,[6] it was found that over the temperature range of about 362
C to 830
C, the Pr3Pt4 phase occurs at an eutectoid decomposition into neighboring phases PrPt and PrPt2. This phenomenon has attracted our attention, so we want to pursue further research to determine whether the analogous decomposition can occur for other trivalent rare earths. [1]

II.

EXPERIMENTAL

The samples of R3Pt4 (R = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Y, Ho, Er) with a total mass of about 1 g were prepared by melting under purified argon. The purity of the ingredients is better than 99.9 wt pct. They were remelted not less than 4 times to ensure homogeneity. The mass losses during arc melting were less than 0.5 wt pct. Then, the samples were sealed in quartz tubes pre-evacuated and refilled with purified argon and then annealed at 900
C for 2 weeks. After homogenizing, the ampoules with samples were quenched into water. CH.F. XU and Y.Y. LIN, Research Scholars, and X.M. LIU, Professor, are with the Department of Mechanical Engineering, Guilin College of Aerospace Technology, Guilin, Guangxi 541004, People’s Republic of China. Contact e-mail: [email protected] Z.F. GU, G. CHENG, and H.Y. ZHOU, Professors, and J. REN, Research Scholar, are with the Department of Information Materials Science and Engineering, Guilin University of Electronic Technology, Guilin, Guangxi 541004, People’s Republic of China. Manuscript submitted May 7, 2009. Article published online October 29, 2009 METALLURGICAL AND MATERIALS TRANSACTIONS A

The phase components of the samples were analyzed by h-2h type X-ray diffractometer (D8 Advance, Bruker AXS GmbH, Karlsruhe, Germany) with Cu Ka radiation. For measurement of unit cell parameters, scans were made between 20 and 90 deg with a step size of 0.02 deg, a step counting time of 0.3 seconds, a 1 deg divergence slit, and a 0.2 deg receiving slit. Silicon was used as an internal standard to correct all observed 2h angles. The weighted average wavelength (1.54178) of Cu Ka radiation was used to convert low and moderate 2h angles to d values. Where the diffraction lines were resolved clearly into a1 and a2 components, the a1 wavelength (1.54056) was used. For each sample, d values from all reflections were used in a computer program designed to calculate a least-squares refinement of lattice dimensions.[7] All reflections were chosen. Corrected d values were used in conjunction with a 1/d2 weight factor to minimize the larger errors inherent at lower angles. To determine the thermal effects and decomposition temperature of an eutect