Pressure Effect on the Structural Transition and Suppression of the High-Spin State in the Triple-Layer $T^{\prime }\mathrm{\text{−}}{\mathrm{La}}_4{\mathrm{Ni}}_3{\mathbf{O}}_8$

We report a comprehensive high-pressure study on the triple-layer $T^{\prime }\mathrm{\text{−}}{\mathrm{La}}_4{\mathrm{Ni}}_3{\mathrm{O}}_8$ with a suite of experimental probes, including structure determination, magnetic, and transport properties up to 50 GPa. Consistent with a recent ab inito calculation, application of hydrostatic pressure suppresses an insulator-metal spin-state transition at $P_c\approx 6\mathrm{GPa}$. However, a low-spin metallic phase does not emerge after the high-spin state is suppressed to the lowest temperature. For $P>20\mathrm{GPa}$, the ambient $T^{\prime }$ structure transforms gradually to a $T^{†}$-type structure, which involves a structural reconstruction from fluorite $\mathrm{La}\mathrm{\text{−}}{\mathrm{O}}_2\mathrm{\text{−}}\mathrm{La}$ blocks under low pressures to rock-salt LaO-LaO blocks under high pressures. Absence of the metallic phase under pressure has been discussed in terms of local displacements of ${\mathrm{O}}^{2-}$ ions in the fluorite block under pressure before a global $T^{†}$ phase is established.

Figure 1

Crystal structures of the Ruddlesden-Popper phase ${\mathrm{La}}_4{\mathrm{Ni}}_3{\mathrm{O}}_{10}$, $T^{\prime }$ phase, and $T^{†}$ phase of ${\mathrm{La}}_4{\mathrm{Ni}}_3{\mathrm{O}}_8$.

Figure 2

Temperature dependence of (a) magnetization with $H=5\mathrm{T}$; the zero-field-cool and field-cool curves overlap (b) resistivity, (c) thermoelectric power, and (d)–(f) lattice parameters for $T^{\prime }\mathrm{\text{−}}{\mathrm{La}}_4{\mathrm{Ni}}_3{\mathrm{O}}_8$. Error bars in these plots are smaller than symbols. Lattice parameters at $T>T_t$ are fit with a polynomial formula.

Figure 3

Temperature dependence of resistivity for $T^{\prime }\mathrm{\text{−}}{\mathrm{La}}_4{\mathrm{Ni}}_3{\mathrm{O}}_8$ under different pressures. Solid lines in Fig. 3c are to guide the eyes. Curves presented as thick lines were obtained with a cubic multianvil device. See the Supplemental Material [10] for detailed clarification.

Figure 4

(a) Temperature dependence of the magnetization under different pressures; (b) the temperature-pressure phase diagram of $T^{\prime }\mathrm{\text{−}}{\mathrm{La}}_4{\mathrm{Ni}}_3{\mathrm{O}}_8$.

Figure 5

(a) SXRD patterns at room temperature under different pressures; (b) Lattice parameters as a function of pressure; lines inside the $V(P)$ curve are results of the curve fitting to the Birch-Murnaghan equation.