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Description
This study is devoted to the investigation of low-temperature thermal properties of phosphate glasses $DyₓY₁₋ₓ(PO₃)₃$ containing different concentrations of rare-earth $Dy³⁺$ ions. The gradual substitution of $Y³⁺$ by $Dy³⁺$ is expected to modify the local structure of the glass network and influence its thermal properties. A series of $DyₓY₁₋ₓ(PO₃)₃$ samples with $Dy³⁺$ content (x = 0, 0.0001, 0.001, 0.01, 0.1, 1) was studied by means of heat capacity and thermal conductivity measurements. The heat capacity $C_p$ was measured using the relaxation technique in the temperature range from 0.4 to 20 K under magnetic fields up to 9 T. Thermal conductivity $κ(T)$ was determined by the two-probe method between 1.8 and 300 K.
The heat capacity data reveal a pronounced boson peak in the $C_p/T^3$ representation for all investigated compositions, confirming the presence of universal low-energy excitations typical of glassy systems. In Dy-doped samples, an additional Schottky-type anomaly is observed due to the splitting of the $Dy³⁺$ energy levels.
The thermal conductivity exhibits characteristic glass-like behavior, including a plateau between approximately 5 and 20 K. Below 5 K, κ(T) follows an approximately quadratic temperature dependence, while above 15 K it gradually increases. The incorporation of $Dy³⁺$ ions modifies phonon transport and changes the absolute values of thermal conductivity in a nontrivial way depending on concentration x. The observed behavior suggests that structural modifications induced by $Dy³⁺$ incorporation, together with magnetic scattering and spin-phonon interactions, play an important role in determining the thermal transport of $Dy³⁺$-doped phosphate glasses.
