This investigation employed microwave whispering-gallery mode (WGM) analysis to characterize the dielectric properties of a cylindrical, single-crystal sample of calcium tungstate (${\mathrm{Ca}\mathrm{WO}}_4$). Through investigation of quasi-transverse-magnetic and quasi-transverse-electric mode families, we can assess loss mechanisms and relative permittivity from room temperature to cryogenic conditions. We report the biaxial permittivity values of ${\epsilon }_{||}^{295\mathrm{K}}=9.029\pm 0.009$ and ${\epsilon }_{\perp }^{295\mathrm{K}}=10.761\pm 0.011$ at room temperature, and ${\epsilon }_{||}^{4\mathrm{K}}=8.794\pm 0.009$ and ${\epsilon }_{\perp }^{4\mathrm{K}}=10.440\pm 0.010$ at liquid-helium temperature. Components are denoted with respect to the $c$-axis of the crystal unit cell. The parallel component agrees well with the published literature at megahertz frequencies; however, the measured perpendicular component is 4.8% lower. The WGM technique offers greater precision, with accuracy limited primarily by the uncertainty in the crystal’s dimensions. WGMs also serve as sensitive probes of lattice dynamics, enabling the monitoring of temperature-dependent loss mechanisms. At room temperature, the measured loss tangents were $\tan {\delta }_{||}^{295\mathrm{K}}=(4.1\pm 1.4)\times {10}^{-5}$ and $\tan {\delta }_{\perp }^{295\mathrm{K}}=(3.64\pm 0.92)\times {10}^{-5}$. Upon cooling to 4 K, the loss tangents improved by approximately two orders of magnitude, reaching $\tan {\delta }_{||}^{4\mathrm{K}}=(1.56\pm 0.52)\times {10}^{-7}$ and $\tan {\delta }_{\perp }^{4\mathrm{K}}=(2.05\pm 0.79)\times {10}^{-7}$. These cryogenic values are higher than those reported in prior studies, likely due to a magnetic loss channel associated with an unidentified paramagnetic spin ensemble. These findings have implications for the use of ${\mathrm{Ca}\mathrm{WO}}_4$ in applications such as spin-based quantum systems and cryogenic bolometry.

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• Dielectric properties
• Permittivity
• Dielectrics
• Transition metal oxides
• Cryogenics
• Microwave techniques
• Scintillators
• Whispering gallery mode resonators