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arXiv · 0904.1582

Large Low Temperature Specific Heat in Pyrochlore Bi$_2$Ti$_2$O$_7$

Brent C. Melot·Ronald Tackett·Jim O'Brien·Andrew L. Hector·Gavin Lawes·Ram Seshadri·Arthur P. Ramirez
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Abstract

Both amorphous and crystalline materials frequently exhibit low temperature specific heats in excess of what is predicted using the Debye model. The signature of this excess specific heat is a peak observed in $C/T^3$ \textit{versus} $T$. To understand the curious absence of long-range ordering of local distortions in the crystal structure of pyrochlore Bi$_2$Ti$_2$O$_7$, we have measured the specific heat of crystalline Bi$_2$Ti$_2$O$_7$ and related compounds. We find that the peak in $C/T^3$ versus $T$ in Bi$_2$Ti$_2$O$_7$ falls at a substantially lower temperature than other similar compounds, consistent with the presence of disorder. This thermodynamic evidence for disorder in crystalline Bi$_2$Ti$_2$O$_7$ is consistent with quenched configurational disorder among Bi lone pairs produced by geometrical frustration, which could represent a possible realization of "charge ice".

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Brent C. Melot, Ronald Tackett, Jim O'Brien, Andrew L. Hector, Gavin Lawes, Ram Seshadri, Arthur P. Ramirez. 2009-04-09. Large Low Temperature Specific Heat in Pyrochlore Bi$_2$Ti$_2$O$_7$. https://doi.org/10.1103/physrevb.79.224111

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