Electronic and Crystal Structures of YbInCu4-Based Compounds under Pressure

The electronic structures of YbInCu4, Y0.1Yb0.9InCu4, YbIn0.95Ag0.05Cu4, and YbIn0.9Ag0.1Cu4 were measured under pressure at 300 K. The Yb valence of Y0.1Yb0.9InCu4 increases gradually with pressure up to 27 GPa. In YbInCu4 and YbIn0.9Ag0.1Cu4, the anomalous Yb-valence decrease under pressure without a structural phase transition was observed for the first time. In YbInCu4 the Yb valence started to decrease above 15 GPa and in YbIn0.9Ag0.1Cu4 it decreased in the pressure range of 5-21 GPa. The anomalous decrease in Yb valence was enhanced at 13 K in a similar high-pressure range. We analyzed and compared the XRD patterns of YbInCu4 and Y0.1Yb0.9InCu4 under high pressure. No structural phase transition was observed in the pressure below 53 GPa for YbInCu4 and 30 GPa for Y0.1Yb0.9InCu4. For YbInCu4 the results showed an anomaly in the pressure dependence of the volume. This could increase the c-f hybridization, resulting in a decrease in the Yb valence and thus correlating it with the anomalous valence crossover.