Crystal structures, frustrated magnetism, and chemical pressure in Sr-doped <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Ba</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:mi>Ni</mml:mi><mml:msub><mml:mi>Sb</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>9</mml:mn></mml:msub></mml:mrow></mml:math> perovskites

The effects of chemical pressure on the structural and magnetic properties triple perovskite ${\mathrm{Ba}}_{3}\mathrm{Ni}{\mathrm{Sb}}_{2}{\mathrm{O}}_{9}$ are investigated by substituting ${\mathrm{Sr}}^{2+}$ ions for ${\mathrm{Ba}}^{2+}$ ions. Two ${\mathrm{Ba}}_{3\ensuremath{-}x}{\mathrm{Sr}}_{x}\mathrm{Ni}{\mathrm{Sb}}_{2}{\mathrm{O}}_{9}$ phases could be stabilized via a solid-state reaction at ambient (AP) in air. $6H$ with ${\mathrm{Sb}}_{2}{\mathrm{O}}_{9}$ pairs $(x=0)\ensuremath{\rightarrow}6H$ $\mathrm{NiSb}{\mathrm{O}}_{9}$ $(x=0.5)\ensuremath{\rightarrow}3C$ (cubic corner-sharing octahedral, $x=1.25$) sequence occurs increasing Sr content, i.e., pressure, which is like that previously reported pure samples obtained under high physical (HP). For $6H {\mathrm{Ba}}_{2.5}{\mathrm{Sr}}_{0.5}\mathrm{Ni}{\mathrm{Sb}}_{2}{\mathrm{O}}_{9} (x=0.5)$ phase, using combined Rietveld refinements powder x-ray neutron diffraction patterns, precession electron tomography data collected thin crystals, aberration-corrected high-angle annular dark field scanning transmission microscopy coupled to energy dispersive spectroscopy mapping, we reach conclusion structure features $\mathrm{Sb}{\mathrm{O}}_{6}$ octahedra face-shared (or Ni-Sb dumbbells) either random orientation dumbbells or nanosized correlations dumbbell arrangement. As observed HP produced through synthesis 9 GPa, AP ${\mathrm{Ba}}_{1.75}{\mathrm{Sr}}_{1.25}\mathrm{Ni}{\mathrm{Sb}}_{2}{\mathrm{O}}_{9} (x=1.25)$ crystallizes $3C$ double ${A}_{2}B{B}^{\ensuremath{'}}{\mathrm{O}}_{6}$ cubic where $A, B$, ${B}^{\ensuremath{'}}$ sites occupied (Ba + Sr), Sb, $(\frac{2}{3}\mathrm{Ni}+\frac{1}{3}\mathrm{Sb})$ atoms, respectively. sites, randomly spin-1 ${\mathrm{Ni}}^{2+}$ diamagnetic ${\mathrm{Sb}}^{5+}$, form face-centered-cubic (FCC) sublattice amount stays above site percolation threshold. Weiss temperatures ($\ensuremath{\approx}\ensuremath{-}65$ $\ensuremath{\approx}\ensuremath{-}213$ K ${\mathrm{Ba}}_{2.5}{\mathrm{Sr}}_{0.5}\mathrm{Ni}{\mathrm{Sb}}_{2}{\mathrm{O}}_{9}$ ${\mathrm{Ba}}_{1.75}{\mathrm{Sr}}_{1.25}\mathrm{Ni}{\mathrm{Sb}}_{2}{\mathrm{O}}_{9}$, respectively) indicate dominant interactions between spins antiferromagnetic magnitudes those corresponding ${\mathrm{Ba}}_{3}\mathrm{Ni}{\mathrm{Sb}}_{2}{\mathrm{O}}_{9}$. compound, {\mathrm{Ba}}_{2.5}{\mathrm{Sr}}_{0.5}\mathrm{Ni}{\mathrm{Sb}}_{2}{\mathrm{O}}_{9}$, muon spin relaxation $(\ensuremath{\mu}\mathrm{SR})$ measurements identify dynamic state down base temperature (95 mK), consistent published inelastic scattering study. $3C {\mathrm{Ba}}_{1.75}{\mathrm{Sr}}_{1.25}\mathrm{Ni}{\mathrm{Sb}}_{2}{\mathrm{O}}_{9}, \ensuremath{\mu}\mathrm{SR}$ $^{121}\mathrm{Sb}$ nuclear resonance both presence transition static below $11(1)$ significant disorder this frozen state, contrast spin-liquid suggested phase Consistently, broad maximum specific heat same temperature. Building data, {\mathrm{Ba}}_{3}\mathrm{Ni}{\mathrm{Sb}}_{2}{\mathrm{O}}_{9}$ {\mathrm{Ba}}_{2.5}{\mathrm{Sr}}_{0.5}\mathrm{Ni}{\mathrm{Sb}}_{2}{\mathrm{O}}_{9}$ discussed light recent works triangular ${J}_{1}\text{\ensuremath{-}}{J}_{2}$ honeycomb systems without quenched disorder. We led driving force toward spin-liquid-like needs incorporated models. Our evidence ground Sr-doped line models geometrically frustrated FCC antiferromagnets. This calls better experimental possibly theoretical understanding phase.