<p>A₂B₂O₇ high-entropy oxides are ceramic materials characterized by diverse compositions, strong structural inclusivity, and a broad range of potential applications. These materials hold significant value in fields such as thermal barrier coatings, energy storage, dielectric materials, and transparent ceramics. However, there are limited reports on the dielectric properties of A₂B₂O₇ high-entropy oxides. Consequently, further investigation is required to understand the polarization mechanisms in high-entropy ceramics and analyze the formation of oxygen vacancies and their influence. In the present study, La₂[(TiZrSnHfGe)_{(1−2<i>x</i>)/5}(NbGa)_<i>x</i>]₂O₇ (<i>x</i> = 0.129, 0.143, 0.157, 0.171) (LTZSHGNGO) ceramics were synthesized successfully using a conventional solid-state reaction method. Compared with La₂(TiZrSnHfGe)₂O₇ ceramics, LTZSHGNGO demonstrated a nearly 6.7-fold increase in dielectric constant and a 33% reduction in dielectric loss. The incorporation of Nb/Ga enhanced the high-temperature dielectric properties and improved dielectric stability. The exceptional dielectric performance is primarily attributed to the synergistic high-entropy effect, while Nb/Ga doping increased the number of oxygen vacancies and generated more defect dipole clusters [Ti⁴⁺·e-<InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12598_2025_3356_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="27" /> </InlineMediaObject> <EquationSource Format="TEX">\({\text{V}}_{\text{O}}^{\bullet \bullet }\)</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mtext>V</mtext> <mrow> <mtext>O</mtext> </mrow> <mrow> <mo>∙</mo> <mo>∙</mo> </mrow> </msubsup> </math></EquationSource> </InlineEquation>-Ti⁴⁺·e]. This study provides novel insights into the dielectric properties of LTZSHGNGO high-entropy ceramics and offers a novel approach to understanding the performance of A₂B₂O₇ ceramics.</p> Graphical abstract <p></p>