Abstract Polycrystalline samples of tantalum and vanadium single and double substituted hexagonal potassium tungsten bronzes (K-HTB’s) with nominal compositions of K_0.3(W⁶⁺ _0.7W⁵⁺ _0.3–yTa⁵⁺ _y)O₃ (0≤y≤0.3), K_0.3(W⁶⁺ _0.7W⁵⁺ _0.3–y V⁵⁺ _y)O₃ (0≤y≤0.18) and K_0.3(W⁶⁺ _0.7W⁵⁺ _0.3–yTa⁵⁺ _y/2V⁵⁺ _y/2)O₃ (0≤y≤0.3) were synthesized by solid state reactions in quartz tubes at 10^–7 MPa and 1073 K. The applied synthesis condition allowed K_0.3WO₃ to crystallize in space group P6₃22, confirmed by X-ray powder diffration and Raman spectroscopic analyses. In this K-HTB composition, W⁵⁺ could fully be replaced by Ta⁵⁺, whereas V⁵⁺ could only be substituted up to y=0.16. The degree of W⁵⁺ substitution was explained in terms of second-order Jahn–Teller (SOJT) distortion of the d⁰ cations W⁶⁺, Ta⁵⁺ and V⁵⁺. The applied distortion index also demonstrates why a complete substitution of W⁵⁺ in K_0.3(W⁶⁺W⁵⁺)O₃ was allowed by a concomitant sharing of Ta⁵⁺ and V⁵⁺, which are statistically distributed on the W⁵⁺/W⁶⁺ sites. As W⁵⁺(d¹) is not SOJT susceptible, it is also shown that the concentration of W⁵⁺ in tungsten bronzes plays an important role in the local WO₆ octahedral symmetry as well as in its coordination.