Evidence of nickel ions dimerization in NiWO<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.svg"><mml:msub><mml:mrow /><mml:mn>4</mml:mn></mml:msub></mml:math> and NiWO<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.svg"><mml:msub><mml:mrow /><mml:mn>4</mml:mn></mml:msub></mml:math>-ZnWO<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.svg"><mml:msub><mml:mrow /><mml:mn>4</mml:mn></mml:msub></mml:math> solid solutions probed by EXAFS …

The existence of exchange-coupled Ni$^{2+}$ ions -- the so-called magnetic dimers in wolframite-type NiWO$_4$ and Zn$_c$Ni$_{1-c}$WO$_4$ solid solutions with high nickel content was discovered by X-ray absorption spectroscopy combined reverse Monte Carlo (RMC) simulations. Temperature- (10--300 K) composition-dependent x-ray spectra were measured at Ni K-edge, Zn W L$_3$-edge microcrystalline NiWO$_4$, ZnWO$_4$. Structural models obtained from simultaneous analysis extended fine structure (EXAFS) three metal edges using RMC radial distribution functions for different atomic pairs made it possible to trace detail changes local environment effect thermal disorder. Dimerization within quasi-one-dimensional zigzag chains [NiO$_6$] octahedra evidenced whole studied temperature range. It manifests itself as splitting Ni-Ni function into two separate peaks. is further preserved $c \leq 0.6$, which related probability find neighboring positions.