Metal-insulator transition in Nd1−xEuxNiO3: Entropy change and electronic delocalization

Abstract

The metal-insulator (MI) phase transition in Nd 1-x Eu x NiO 3 , 0 x 0.35, has been investigated through the pressure dependence of the electrical resistivity q(P, T) and measurements of specific heat C P (T). The MI transition temperature (T MI) increases with increasing Eu substitution and decreases with increasing pressure. Two distinct regions for the Eu dependence of dT MI /dP were found: (i) for x 0.15, dT MI /dP is nearly constant and $À4.3 K/kbar; (ii) for x ! 0.15, dT MI /dP increases with x and it seems to reach a saturation value $À6.2 K/kbar for the x ¼ 0.35 sample. This change is accompanied with a strong decrease in the thermal hysteresis in q(P, T) between the cooling and warming cycles, observed in the vicinity of T MI. The entropy change (DS) at T MI for the sample x ¼ 0, estimated by using the dT MI /dP data and the Clausius-Clapeyron equation, resulted in DS $ 1.2 J/mol K, a value in line with specific heat measurements. When the Eu concentration is increased, the antiferromagnetic (AF) and the MI transitions are separated in temperature, permitting that an estimate of the entropy change due to the AF/Paramagnetic transition be carried out, yielding DS M $ 200 mJ/mol K. This value is much smaller than that expected for a s ¼ 1/2 spin system. The analysis of q(P, T) and C P (T) data indicates that the entropy change at T MI is mainly due to the electronic delocalization and not related to the AF transition.

Superconducting Nd 1− x Eu x NiO 2 thin films using in situ synthesis

“…3A). The transition occurs at 230 K in an x = 0.2 Nd 1−x Eu x NiO 3 sample and at 280 K in an x = 0.3 sample, consistent with previous reports (27).…”

Structural investigation of the insulator-metal transition in NiS$_{2-x}$Se$_x$ compounds

“…As this firstorder transition can be attributed to various origins, it is important to point out that the entropy change 32 by the volume contraction is tiny [i.e., only about 0.2 % for the temperature shown in Figs. 3(c-d)], and is comparable with other materials proposed in terms of the electronic-driven transition 31 . Also, our Raman measurements revealed only a slight monotonic shift in the stretching frequencies near the transition temperature, thus decreasing the likelihood of a significant contribution to the entropy (in sharp contrast to (chromiumdoped) V 2 O 3 29 ).…”

“…The sudden drop in a c (with the volume decrease) with decreasing temperature, which concurs with the transition 30,31 , can be understood by the Clausius-Clapeyron relation 16,31 , an equation describing the entropy change between insulating and metallic phases. The calculated entropy change (from the x = 0.49 data shown in Fig.…”

Anisotropic character of the metal-to-metal transition in Pr4Ni3O10

“…We note, however, that there is no detectable hysteresis around 𝑇𝑇 𝑝𝑝𝑝𝑝 within the temperature resolution of the measurement (≈ 0.5 K) [Fig. S1], and that a value of ΔS lower than Rln(2) is often observed at phase transition in metallic nickel oxides [52].…”