Specific heats of the pyrochlore compounds Y2Mo2O7 and Y2Ru2O7

Abstract

The specific heats of the pyrochlore compounds Y2Mo2O7 were measured below 20 K. The Y2Ru2O7 data were found to be well described by the expression C=γT+αT3 below 7 K with a γ value of 2.92±0.1 mJ/mole K2 and an α value of 0.236±0.015 mJ/mole K4. A correct description for the Y2Mo2O7 data was not obvious since there was, in addition to γT+αT3 contributions, a Schottky-like term with a maximum near 12 K plus a smaller contribution near 3.5 K of unknown origin. The γ and α values of 1.33±1 mJ/mole K2 and 0.973±0.06 mJ/mole K4, respectively, should be used with caution. Neutron diffraction data were taken at 300, 77, 13, and 4.2 K on Y2Mo2O7. The results indicated that no transition to an antiferromagnetically ordered state occurred down to 4.2 K.

Specific Heat and ac Susceptibility Studies on Ruthenium Pyrochlores R2Ru2O7 (R=Rare Earths)

“…At low temperatures, the speci"c heat C can be well described by the relation C" ¹# ¹. The values of for these two compounds are determined by the least squares "tting in the temperature range below 7 K. They are 5 (for Y Ru O ) and 3 (for Lu Ru O ) mJ/K mol, which are good in agreement with the results reported previously (3,4). These experimental results are contrastive to the case for the spinglass molybdenum pyrochlore (5), where a broad peak is seen at its spin-glass transition temperature in the speci"c heat vs temperature curve.…”

Hubbard-corrected oxide formation enthalpies without adjustable parameters

“…Debye model fits for the corrections of Y and Ru are based on data in [59], and also O 2 is corrected analogously to the other oxide heats of formation. A low-temperature heat capacity fit yielding a Debye temperature of 449 K for Y 2 Ru 2 O 7 is taken from [67]. Low and moderate-temperature heat capacity data from [68] and [66], respectively, is used in the integral (11) to determine the entropy at 298 K of ∼216 JK −1 mol −1 and fit the parameter y of the Debye model for T = 0 extrapolation and subtraction of E ZP .…”

Liquidlike correlations in single-crystalline Y2Mo2O7: An unconventional spin glass

“…This highly frustrated sublattice topology is the culprit behind the richness of the magnetic ground states (Figure 1b, c). Some of the earlier reported syntheses of Y 2 Mo 2 O 7 (S=1) pyrochlore stem back to 1980 [24] where the electrical properties and specific heat [25] were examined in conjunction with other pyrochlores. It was first shown by Reimers et al and Greedan et al [26,27] that Y 2 Mo 2 O 7 displays all the characteristics of typical spin glass behavior below the freezing temperature of T f =22.5 K [9,[27][28][29][30].…”