Using first-principles calculations, we study the electronic structure of an unexplored Zintl compound, KCdBi. Our calculations establish KCdBi to be a rare example of a strong $Z_2$ topological semimetal. The compound is found to be cleavable with a small cleavage energy ($\sim 0.2\mathrm{J}/{\mathrm{m}}^2$). The nanostructured KCdBi obtained by cleaving turned out to be a topological insulator, causing a semimetal to insulator transition upon dimensionality reduction. A rich phase diagram emerges upon application of an electric field to nanostructured KCdBi, which consists of topological insulating, $Z_2$ topological metallic, weak and strong Rashba phases. This compound thus offers a platform to study nontrivial properties tunable by electric field and dimensionality. Our findings are expected to stimulate experimental investigation of this interesting compound.

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• Electrical properties
• First-principles calculations
• Topological materials