H. Shahed^1,2, M. Ocker³, C. Krellner³, K. Kliemt³, and Michael Merz^{1, 4}

¹Institute for Quantum Materials and Technologies, Karlsruhe Institute of Technology, Kaiserstr. 12, 76131 Karlsruhe, Germany

² Jülich Center for Neutron Science–2/Peter Grünberg Institut, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany

³Kristall- und Materiallabor, Physikalisches Institut, Goethe-Universität Frankfurt, Max-von-Laue Stasse 1, 60438 Frankfurt am Main, Germany

⁴Karlsruhe Nano Micro Facility (KNMFi), Karlsruhe Institute of Technology, Kaiserstr. 12, 76131 Karlsruhe, Germany

The interplay between valence changes and structural degrees of freedom in Eu-based intermetallics provides a rich platform for studying endpoint criticality, lattice collapse transitions, and electronic instabilities directly coupled to the lattice. We present a comprehensive investigation of the Eu(Pd_1-xPt_x)₂Si₂ (x = 0, 0.05, 0.10, 0.15, 0.2) series, where Pt substitution tunes the valence instability of Eu and drives the system across a critical endpoint. High-resolution temperature-dependent single-crystal X-ray diffraction reveals that at low substitution levels, Eu undergoes a smooth valence crossover, while for x = 0.10, the transition becomes sharp and undergoes first-order. Furthermore, investigations on disordered EuPd_2-ySi_2+y (y = 0.10, 0.16) demonstrate how small off-stoichiometries suppress the valence transition and lead to conventional thermal contraction behaviour. Our results establish chemical substitution and disorder as effective tuning parameters to access the valence-transition critical point in this class of materials [1]–[4] paving the way for future high-pressure and magnetic studies.

Reference

[1] K. Kliemt et al., “Influence of the Pd − Si Ratio on the Valence Transition in EuPd₂Si₂ Single Crystals,” 2022, doi: 10.1021/acs.cgd.2c00475.

[2] M. Ye et al., “PHYSICAL REVIEW B 107 , 195111 ( 2023 ) Strong electron-phonon coupling and enhanced phonon Grüneisen parameters in valence-fluctuating metal EuPd₂Si₂,” vol. 195111, pp. 1–7, 2023, doi: 10.1103/PhysRevB.107.195111.

[3] M. Peters et al., “PHYSICAL REVIEW MATERIALS 7 , 064405 ( 2023 ) From valence fluctuations to long-range magnetic order in EuPd₂(Si_1-xGe _x) ₂ single crystals,” vol. 064405, pp. 1–11, 2023, doi: 10.1103/PhysRevMaterials.7.064405.

[4] M. Ocker et al., “Single crystal growth and properties of Au- and Ge-substituted EuPd₂Si₂,” pp. 1–16, 2026.