Structural and dielectric properties of yttrium substituted nickel ferrites

•Dense NiFe2−xYxO4 ceramics (with 0≤x≤0.3) were prepared.•Pure spinels were obtained for x≤0.07 while for x≥0.15 samples had secondary phases.•With addition of yttrium, ac conductivity slightly increased.•We suggest several effects that can explain the observed changes in ac conduction.•With addition of yttrium, dielectric constant increased while the tgδ decreased.