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Recently, the low-temperature phase of water molecules confined within nanocages formed by the crystalline lattice of water-containing cordierite crystals has been reported to comprise domains with ferroelectrically ordered dipoles within the a, b-planes which are antiferroelectrically alternating along the c-axis. In the present work, comprehensive broad-band dielectric spectroscopy is combined with specific heat studies and molecular dynamics and Monte Carlo simulations in order to investigate in more detail the collective modes and single-particle excitations of nanoconfined water molecules. From DFT-MD simulations we reconstruct the potential-energy landscape experienced by the H2O molecules. A rich set of anisotropic temperature-dependent excitations is observed in the terahertz frequency range. Their origin is associated with the complex rotational/translational vibrations of confined H2O molecules. A strongly temperature dependent relaxational excitation, observed at radio-microwave frequencies for the electric field parallel to the crystallographic a-axis, E‖‖a is analyzed in detail. The temperature dependences of loss-peak frequency and dielectric strength of the excitation together with specific heat data confirm a ferroelectric order–disorder phase transition at T0 ≈ 3 K in the network of H2O dipoles. Additional dielectric data are also provided for polarization E‖‖b, too. Overall, these combined experimental investigations enable detailed conclusions concerning the dynamics of the confined water molecules that develop within their microscopic energy landscapes. [ABSTRACT FROM AUTHOR]

We report a detailed study of the polymorphic transitions in ternary stannide CeRuSn on high quality single crystals through a combination of x-ray diffraction experiments conducted at 300, 275, and 120 K, and measurements of the thermal expansion, magnetization, and resistivity, along main crystallographic axes. In addition, the transition was followed as a function of pressure up to 0.8 GPa. The present x-ray diffraction data show that the room temperature polymorph consists of the lattice doubled along the c axis with respect to the CeCoAl-type structure consistent with previous reports. Upon cooling, the compound undergoes two successive transitions, first to a quintuple (~290 K) and than to a triple CeCoAl superstructure at ~225 K. The transitions are accompanied by a tremendous volume change due to a strong shrinking of the lattice along the c axis, which is clearly observed in thermal expansion. We advance arguments that the volume collapse originates from an increasing number of crystallographically inequivalent Ce sites and the change of ratio between the short and long Ce-Ru bonds. The observed properties of the polymorphic transition in CeRuSn are reminiscent of theɣ--ɑ transition in elementary cerium, suggesting that similar physics, i.e., a Kondo influenced transition and strong lattice vibrations, might be the driving forces. [ABSTRACT FROM AUTHOR]

We report on single crystal growth and crystallographic parameters results of Ce2PdIn8, Ce3PdIn11, Ce2PtIn8 and Ce3PtIn11. The Pt-systems Ce2PtIn8 and Ce3PtIn11 are synthesized for the first time. All these compounds are member of Ce n T m In3n+2m (n=1, 2,..; m=1, 2,.. and T= transition metal) to which the extensively studied heavy fermion superconductor CeCoIn5 belongs. Single crystals have been grown by an In self-flux method. Differential scanning calorimetry studies were used to derive optimal growth conditions. Evidently, the maximum growth conditions for these materials should not exceed 750°C. Single crystal x-ray data show that Ce2 TIn8 compounds crystallize in the tetragonal Ho2CoGa8 phase (space group P4/mmm) with lattice parameters a=4.6898(3)Å and c=12.1490(8)Å for Pt-based one (Pd: a=4.6881(4)Å and c=12.2031(8)Å). Ce3 TIn11 compounds adopt Ce3PdIn11 structure with a=4.6874(4)Å and c=16.8422(12)Å for Pt-based one (Pd: a=4.6896Å and c=16.891Å). Specific heat experiments on Ce3PtIn11 and Ce3PdIn11 have revealed that both compounds undergo two successive magnetic transitions at T 1 ~2.2K followed by T N ~2.0K and T 1 ~1.7K and T N ~1.5K, respectively. In addition, both compounds exhibit enhanced Sommerfeld coefficients yielding γ Pt=0.300J/molK2 Ce (γ Pd=0.29J/molK2 Ce), hence qualifying them as heavy fermion materials. [ABSTRACT FROM AUTHOR]