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Which metals form completely mixable alloys with potassium?

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A periodic table element box for potassium shows atomic number 19, symbol K, atomic weight 39.0983, electron configuration [Ar]4s1, and name potassium. Icons indicate it is an alkali metal, solid at room temperature, body-centered cubic crystal structure, and has strongly basic higher-valence oxides. A key explains the symbols for alkali metals, solid state, body-centered cubic structure, and strong basicity. — potassium Properties of potassium.

Potassium forms completely mixable alloys (forming complete solid solutions and mixed crystals) with the other heavier alkali metals, specifically rubidium and cesium.12

These elements are able to mix completely because they possess similar atomic volumes and ionization energies. While potassium also forms alloys with sodium, these systems are typically eutectic rather than completely miscible due to the significant difference in atomic size between the two elements.231