Pressure effects on the phase transitions and energy gap in CeRhAs

Abstract

We report on the electrical resistivity, thermal expansion, and x-ray diffraction measurements of singlecrystalline sample of the so-called Kondo semiconductor CeRhAs under pressures up to 3 GPa. This compound undergoes successive structural phase transitions at T 1 = 360, T 2 = 235, and T 3 = 165 K at ambient pressure. On cooling below T 1 , the crystal structure changes from the hexagonal LiGaGe-type to the orthorhombic-TiNiSi-type with a 2b ϫ 2c superlattice. By applying pressure up to 1.5 GPa, T 1 increases with a ratio of 270 K/GPa, whereas both T 2 and T 3 decrease with −100 K / GPa. The concurrent decrease of both the a parameter and the energy gap along the a axis with increasing pressure contradict the c-f hybridization gap model in which the gap is enlarged by the enhancement of hybridization between the 4f electrons and conduction band. Instead, a sort of charge-density-wave transition at T 1 is proposed for the origin of gap formation of this compound. The semiconducting behavior in the resistivity vanishes when the phase with the 2b ϫ 2c superlattice decomposes into two orthorhombic phases below 100 K and above 1.5 GPa.

Cerium intermetallics with TiNiSi-type structure

“…The arsenide CeRhAs [17,35,36,107,108] shows three anomalies (T 1 = 370, T 2 = 235 and T 3 = 165 K) in the temperature dependence of the lattice parameters and also in the magnetic susceptibility data. Closer inspection of the unit cell parameters revealed that this anomaly mainly concerns the a lattice parameter, the pseudo-hexagonal axis along which the Rh 3 As 3 hexagons are stacked.…”

“…As described in the crystal structure part the lattice parameters show three anomalies (T 1 = 370, T 2 = 235 and T 3 = 165 K), which mainly concern the a lattice parameter. Along the a axis zig-zag chains of cerium are formed, and due to the structural changes the hybridization and consequently the physical properties are influenced significantly [35,36]. Before the crystal structure had been completely understood, a gap formation has been attributed to the Kondo temperature.…”

“…High-quality crystals of CePtAl were grown with the Czochralski pulling method using tri-or tetra-arc furnaces [33,34]. The Bridgman technique was used for the growth of CeRhAs and CeRhSb crystals [17,35,36]. For CeRhAs elemental arsenic and a pre-melted ingot of composition CeRh 1.02 were used as starting materials and molybdenum was taken as crucible material.…”

Structure and Properties of Dimorphic CePdZn

“…The ZrNiAl type high-temperature modification [4] transforms to a low-temperature (LT) modification with a new structure type upon annealing the sample at 1170 K [5]. One of the most interesting compounds is the Kondo insulator CeRhAs [6,7] which shows three successive temperature driven phase transition associated with a charge-density-wave and two different modulation vectors. The stannide CeRuSn [8] is a static intermediate-valent system which shows trivalent intermediate-valent ordering at room temperature and a transition to a modulated structure at low temperature.…”

Structure and Magnetic Properties of CePtZn

“…To give an example, in the series CePtIn, CePtSn to CePtSb the magnetic properties change from a heavy fermion system [1] to an 8 K [2] and 4.5 K [3] antiferromagnet. From the intermediatevalent gallide CeRhGa [4], the system changes to the 9.3 K antiferromagnet CeRhGe [5], and CeRhAs [6] is a valence-fluctuating compound. In the platinumbased series we were recently able to further reduce the VEC by substitution of indium by magnesium.…”