Structural transformations in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mrow> <mml:mo>(</mml:mo> <mml:mn>1</mml:mn> <mml:mtext>−</mml:mtext> <mml:mi>x</mml:mi> <mml:mo>)</mml:mo> </mml:mrow> <mml:msub> <mml:mi>Na</

Single crystals of $(1\text{\ensuremath{-}}x){\mathrm{Na}}_{0.5}{\mathrm{Bi}}_{0.5}{\mathrm{TiO}}_{3}\text{\ensuremath{-}}x{\mathrm{BaTiO}}_{3}$ $(\mathrm{NBT}\text{\ensuremath{-}}x\mathrm{BT})$ with a composition below $(x=0.013)$ and above $(x=0.074)$ the morphotropic phase boundary (MPB) were studied by in situ high-pressure x-ray diffraction with synchrotron radiation and Raman spectroscopy. We show that both compounds undergo a reversible pressure-induced phase transition to structures with $Pnma$ symmetry, regardless of their symmetry at ambient conditions. The high-pressure phase resembles that recently reported for ${x}_{\mathrm{MPB}}=0.048$ [Sci. Rep. 14, 18799 (2024)], as the critical pressure ${p}_{\mathrm{c}}$ gradually increases with $x$. However, the pathway of developing the high-pressure phase varies with the composition, revealing distinct ways of Ba incorporation into the NBT matrix for the pseudorhombohedral $(x=0.013)$ and tetragonal $(x=0.074)$ phases. For $x&lt;{x}_{\mathrm{MPB}}$ the ${\mathrm{Ba}}^{2+}$ cations are preferentially accommodated in the tetragonal-type nanodomains existing in the dominant pseudorhombohedral NBT matrix, whereas for $x&gt;{x}_{\mathrm{MPB}}$, ${\mathrm{Ba}}^{2+}$ is dispersed in both the rhombohedral nanodomains and the dominant tetragonal matrix. Furthermore, for $x=0.074$ there are incommensurate structural modulations at ambient pressure, which up to ${p}_{c}$ remain unaffected by pressure, but vanish above ${p}_{c}$.