Ce Compounds Research Articles

Structure and properties of mixed valent CeFe2Al8

Temperature dependent magnetic, electrical transport and thermal properties of polycrystalline orthorhombic CeFe2Al8intermetallic compound have been studied along with its isostructural La counterpart, LaFe2Al8. For the cerium compound, low fielddcmagnetization exhibits an antiferromagnetic like ordering (TN) ∼ 4 K. The main feature of the magnetic susceptibility plot is a broad hump spanning a large temperature range, indicating mixed valence of Ce in the compound, in good agreement with reported literature. However, contrary to the reported observations we find that the mixed valence state is very robust and was evident even up to very high magnetic fields (> 2 T). Further, in this work we report 3d core level photoemission spectra of cerium in CeFe2Al8, to understand the valence state of cerium ions in this system. Additionally, from resistivity measurements it is found that, CeFe2Al8is metallic with no indication of any anomaly, till the lowest temperature of measurement. Specific heat measurements show very low value of heat capacity and electronic contribution. The isostructural La analogue, LaFe2Al8compound shows broadness in susceptibility with maxima around 44 K which may be attributed to ordering of Fe moments. The comparison of Ce and La compounds brings out the role of Fe magnetic moments which may be responsible for competing with cerium moments and resulting in the dilution of long-range magnetic order, also contributing to magnetic frustration in CeFe2Al8.

Elucidation of synergism in Ce-Zr/SBA-15 mesoporous catalysts and the effects on the activity in selective glycerol to lactic acid reaction

The continued conversion of glycerol to value-added chemicals is essential in ensuring the sustainable development of the biodiesel industry. Selective catalytic oxidation of glycerol to lactic acid provides an alternative approach to valorizing glycerol. A mesoporous SBA-15 supported mixed-metallic oxide catalyst is deemed essential to selectively produce lactic acid in this mixed parallel and multi-step reaction. SBA-15-supported bimetallic Ce and Zr oxides were proved to be highly efficient catalysts for the selective glycerol oxidation into lactic acid in base-free media. The synergism between Ce and Zr in the bimetallic oxide compounds could enhance the creation of oxygen vacancies in the catalyst via the reduction of Ce4+ to Ce3+. The 2:1CeZr/SBA-15 catalyst exhibited prominent catalytic activity in selectively oxidizing glycerol to lactic acid, with a glycerol conversion of 91.8% and a lactic acid yield of 35.1%. This work achieved superior catalytic performance compared to previously conducted studies, primarily due to the significantly higher initial glycerol concentration employed in this study. To ascertain the intrinsic active sites of the catalyst, the physicochemical properties of the catalyst were thoroughly examined using BET, FTIR, XRD, FESEM, TEM, CO2-TPD, O2-TPD, and H2-TPR analysis. This work concluded that the synergistic interaction of the active sites, which led to the formation of active oxygen species, facilitated primary dehydrogenation of the terminal -OH bond in glycerol. Hence, in this work, a plausible glycerol conversion mechanism over the 2:1CeZr/SBA-15 catalyst was also proposed.

Thermal stability and luminescence of zinc and lanthanide(Tb3+ and Ce3+) coordination polymers with pyridine-2,5-dicarboxylic acid by the WASSR method

Two sorts of inorganic-organic coordination polymers (Tb2Zn(2,5-PDC)4・10H2O(I), Ce2Zn2(2,5-PDC)5・2H2O(II))constructed by lanthanide(TbIII 、CeIII) and ligand of the pyridine-2,5-dicarboxylate have been prepared by the soft chemical synthesis method(WASSR method). The purpose of this study was to investigate optic property, thermal stability and dehydration/hydration behavior. The experimental results indicated Tb compound(I) show stronger red phosphor than Ce compound(II), but framework of crystal structure is weaker than Ce compound(II) on account of XRD patterns comparison between dehydrated compound and re-hydrated compound. The thermal stability of Ce compound(II) is better than Tb compound(I) owing to the first weight loss temperature is high to Tb compound about 200 °C.

Unusual superconductivity in crystallographically disordered RT2−xSn2 compounds

The discovery of new superconducting materials represents a complementary and crucial tile to shed light on the mechanism controlling the phenomenon of superconductivity. During the search for new superconducting materials, we discovered a new series of intermetallic compounds with the general composition RZn2−xSn2 (R = La, Ce, Pr, Nd). Their formation and crystal structure have been investigated. The Zn content decreases along the series from ≈ 1.50 in LaZn1.50(1)Sn1.98(2) to ≈ 1.32 in NdZn1.321(8)Sn2.01(2), due to the partial occupation of one of the two Zn sites [the Zn1 (2c) site, which from ≈ 50% in the La compound drops to ≈ 42%, ≈ 37% and ≈ 32% in the Ce, Pr and Nd compounds, respectively]. Both the Zn occupation factor and unit cell volume follow the lanthanide contraction. No such compound has been observed with Sm. AC and DC magnetic susceptibility and transport measurements revealed LaZn1.5Sn2 to undergo a sharp superconducting transition at Tc = 5.5 K. In order to search for further possible superconductive homologues, the lanthanum substituted phases La(Zn,T)2–xSn2 (T = Ti, Mn, Fe, Co, Ni, Cu, Pd, Ag, Pt, Au, Cd; x ≈ 0.5) were also prepared. The crystal structure of the ternary compounds is a disordered defective derivative of the tetragonal CaBe2Ge2-type (tP10, P4/nmm), with a partially occupied Zn Wyckoff site and a disordered Sn position. Three related isostructural series, corresponding to three new prototypes, have been identified; they all contain conventional checkered pyramidal layers characteristic of the archetype. The magnetic and transport properties have been measured for some of these substituted quaternary La compounds and we found that superconductivity is preserved in them but in the orthorhombic compounds or when T was a magnetic transition metal (e.g., Ni or Mn). A slight decrease in Tc down to about 4.0 K was detected as a result of the Zn by T atomic substitution.

Facile Oxidation of Ce(III) to Ce(IV) Using Cu(I) Salts.

The synthesis, luminescence, and electrochemical properties of the Ce(III) compound, [(C5Me5)2(2,6-iPr2C6H3O)Ce(THF)], 1, were investigated. Based on the electrochemical data, treatment of 1 with CuX (X = Cl, Br, I) results in the formation of the corresponding Ce(IV) complexes, [(C5Me5)2(2,6-iPr2C6H3O)Ce(X)]. Each complex has been characterized using NMR, IR, and UV-vis spectroscopy as well as structurally determined using X-ray crystallography. Additionally, the treatment of [(C5Me5)2(2,6-iPr2C6H3O)Ce(Br)] with AgF results in the formation of the putative [(C5Me5)2(2,6-iPr2C6H3O)Ce(F)]. The electronic structure of these Ce(IV)-X complexes was investigated by bond analyses and the Ce(IV)-F moiety using quantum chemistry NMR calculations.

RETRACTED: Influence of At%Ce on the electronic structure and mechanical properties of Al–Ce compounds from first-principles calculations

Ce as an additive in aluminum alloys can significantly improve the microstructure and properties of aluminum alloys. However, the structure and the associated overall properties of the Ce-Al binary system are not known. Here, we applied a first-principles approach to investigate the effects of At%Ce on the electronic structure, mechanical and thermodynamic properties of the Ce-Al compounds. The results show that CeAl2 exhibits the best stability at T = 0 K. The electronic structure analysis shows that they are both metallic. The ionic bonding of the Ce-Al compounds gradually weakened with increasing At%Ce. In addition, the Poisson's ratio of the Ce-Al compounds varies in the range of 0.2 and 0.32, and most of the Ce-Al compounds are brittle. The anisotropy results show that all the Ce-Al compounds exhibit more or less elastic anisotropy, where Young's modulus of the Ce-Al compounds has a strong orientation dependence. The obtained Debye temperatures indicate that Ce3Al11 has the strongest covalent bonds and good thermal conductivity.

Ce2Pd21Si6 vs. Ce3Pd20Si6: Effect of Ce/Pd substitution on the physical properties

In this study, polycrystalline intermetallic compounds Ce3-xPd20+xSi6 (x = 0; 0.5; 1) as well as La-based analogues La3-xPd20+xSi6 (x = 0; 1) are synthesized. At the same time, R2Pd21Si6 (RCe, La) are new rare earth compounds presented here. An analysis of the crystal structure shows that the increase in x leads to partial (x = 0.5) or complete (x = 1) replacement of Ce/La ions by Pd in one of the two Wyckoff positions, namely, in position 4a. Ab initio DFT calculations demonstrate good agreement between the determined lattice parameters and those found experimentally for both Ce3-xPd20+xSi6 (x = 0; 0.5; 1) and La3-xPd20+xSi6 (x = 0; 1). A comparative analysis of resistivity and specific heat of Ce3-xPd20+xSi6 with x = 0; 0.5; 1 makes it possible to associate the Ce ions in the 8c position with Kondo behaviour in all three compositions, which manifests itself in an increase in resistivity with cooling, as well as in a broad peak of the magnetic contribution of specific heat. The Kondo temperature TK ≈ 25 K obtained from the analysis of the temperature dependences of the heat capacity turns out to be the same for all Ce compounds. The appearance of cerium ions in the position 4a in compositions with х = 0 and х = 0.5 leads to an additional contribution to the specific heat, the value of which increases with decreasing temperature, as well as, to the formation of a coherent Kondo-lattice state with a maximum of the resistivity at Tcoh ≈ 15 K, followed by the subsequent onset of negative magnetoresistance regime below Tinv≈ 7 K. Apparently, this behaviour is associated with the appearance of spin and orbital correlations proceeding the quadrupole and antiferromagnetic transitions occurring at lower temperatures. Magnetization measurements show more localized character of magnetic moments of Ce ions at T = 2 K in Ce3Pd20Si6 as compared to the Ce2Pd21Si6.

Antioxidative phenolic compounds from the aerial parts of Cyperus exaltatus var. iwasakii and their HPLC analysis

The constituents and antioxidant activities of Cyperus exaltatus var. iwasakii (CE) have not been studied to date. In this study, the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6 sulfonic acid) (ABTS) assays were used to evaluate the radical-scavenging activities of the ethanol extract, four fractions, and isolated compounds of CE. In addition, phenolic acids and flavonoids were isolated from the ethanol extract of CE using column chromatography. The compounds identified by spectroscopy were gallic acid, protocatechuic acid, vanillic acid, p-coumaric acid, rutin, ferulic acid, isoquercitrin, astragalin, quercetin, luteolin, apigenin, tricin, and kaempferol. Quantitative analysis using high-performance liquid chromatography (HPLC) revealed that the major flavonoids of CE were astragalin and tricin and that the major phenolic acid was p-coumaric acid. In addition, comparative analysis of CE from Ganghwa and Hampyeong habitats using HPLC showed that the Hampyeong CE had a higher phytochemical content. Comparative analyses of the isolated compounds were also conducted among five Cyperus species. The highest antioxidant activities were found in the ethyl acetate (EtOAc) fraction, and among the compounds isolated from CE, vanillic acid and quercetin showed remarkable antioxidant activity even when compared with ascorbic acid. The results demonstrate the usefulness of CE, which has not been sufficiently studied previously, and will facilitate the evaluation of its potential effectiveness as antioxidant functional plant material.

Ab initio studies of Electronic Structure and magnetic properties of RAl(Mg)3 (R= Ce, Pr, Nd, Sm and Gd) alloys

We report the magnetic behaviour of RAl3 and R(Mg)3 (R= Ce, Pr, Nd, Sm and Gd) alloys studied through ab initio calculations based on density functional theory (DFT). The magnetic moments obtained from the all electron full potential calculations suggest strong magnetic instability in Ce compounds. The compounds with heavier rare earths (Pr, Nd, and Gd) exhibit local moment with high orbital moment, consistent with crystal field splitting of the 4fn ground state. The results obtained for SmAl3 and SmMg3 suggest possible valence fluctuation. Our calculated magnetic moments closely agree with experimental results reported in literature. We have also calculated the magnetic hyperfine field and its spin and orbital contributions. While, the total hyperfine field is dominated by the contribution from orbital magnetic moment, the Fermi contact contribution to the hyperfine field is found to scale with the spin projection factor (gJ−1)J. The calculated hyperfine field values are found to show good agreement with available experimental results.

Influence of method of synthesis on the colour and NIR reflective properties of bismuth and vanadium doped cerium phosphate

Inorganic pigment with NIR reflectance properties could mitigate the energy consumption used for controlling the indoor temperature in buildings. This work presents an environmentally benign pigment series of Bi3+ and V5+ doped CePO4 of formula Ce1-xBixP1-yVyO4 (x = y = 0.02 to 0.5) by coprecipitation and hydrothermal methods. Doping of metal ion could tune the band gap of CePO4 approximately from 3.01 to 2.4 eV mainly due to the introduction of additional V3d orbital in the conduction band. Doping changed the color of the compound from white to yellow color. The synthesized compounds were characterized by XRD for phase identification, FT-IR for functional group analysis, UV-DRS to determine the sample's reflectance and band gap, CIE – L*a*b* for color values and SEM techniques for morphology studies. XPS analysis was conducted to confirm the oxidation state of Ce, V and Bi in the compound. Among the series of individual and co-doped CePO4 series, the compound Ce0.8Bi0.2(P0.8V0.2O4) synthesized from the precipitation method exhibited a high yellow value (b* = 24.58) with single-phased monoclinic system and 75.05% NIR solar reflectance. The same compound prepared by the hydrothermal method exhibited less yellow value (b* = 18.96) and 75.67% NIR solar reflectance. Good chemical stability in acid and alkaline medium was observed.

Synthesis, Crystal Structure, and Electrical and Magnetic Characterizations of the Monoclinic Compounds Ln3Mo4+xSi1–xO14 (Ln = La, Ce, Pr, and Nd; x = 0 and 0.35) Containing Mo3 Clusters and Mo2 Dimers

Powder samples of the new monoclinic compounds Ln3Mo4SiO14 (Ln = La, Ce, Pr, and Nd) and single crystals of Pr3Mo4.35Si0.65O14 were obtained by the solid-state reaction. The crystal structure of Pr3Mo4.35Si0.65O14 was determined by single-crystal X-ray diffraction. Pr3Mo4.35Si0.65O14 crystallizes in the monoclinic space group P21/n with unit-cell parameters a = 5.6361 (2) Å, b = 17.5814 (8) Å, c = 10.9883 (4) Å, and Z = 4. Full-matrix least-squares refinement on F2 using 7544 independent reflections for 203 refinable parameters results in R1 = 0.0359 and wR2 = 0.0831. The structure contains chains of Mo3O13 clusters and chains of edge-sharing MoO6 octahedra with alternately short (2.508 Å) and long (3.161 Å) Mo-Mo distances running parallel to the a axis that are separated by 8- or 10-coordinate Pr-O polyhedra. Magnetic susceptibility measurements on the Ln3Mo4SiO14 (Ln = La, Ce, Pr, and Nd) are in agreement with a trivalent state of the rare earths for the Ce, Pr, and Nd compounds, while that on the lanthanum compound confirms the presence of one unpaired electron per Mo3 as expected. Resistivity measurements on a single crystal show that Pr3Mo4.35Si0.65O14 is a small band gap semi-conductor.

Origin of negative thermal expansion in strongly correlated f− electron systems

We have investigated the origin of the negative-thermal-expansion (NTE) phenomena observed in various strongly correlated $\mathit{f}\text{\ensuremath{-}}$electron systems, including Ce, Sm, and Yb rare-earth compounds and actinide element Pu. We have thoroughly surveyed existing nonmagnetic $\mathit{f}\text{\ensuremath{-}}$electron NTE materials and identified that the temperature ($T$)-induced valence transition plays an essential role in realizing the NTE in Sm- and Yb-based mixed-valence (MV) systems. We have discussed the contrasting thermal-expansion behaviors between (Sm, Yb)-based MV systems and their electron-hole symmetric counterparts (Ce, Eu)-based MV systems that exhibit positive-thermal-expansion (PTE) phenomena. We have also clarified the origin of intriguing thermal expansion behavior of Pu, which, upon cooling, reveals not only the NTE, but also the strong PTE. Finally, we have predicted the possible existence of an additional NTE feature in topological-Kondo-insulator (TKI) candidates of ${\mathrm{SmB}}_{6}$, g-SmS, and ${\mathrm{YbB}}_{12}$ in the low-$T$ regime where the TKI nature is expected to emerge.

Magnetic properties of rare-earth-lean ThMn12-type (Nd,X)Fe11Ti (X: Y and Ce) compounds: A DFT study

Due to the resource criticality of rare-earths (RE), an alternative to the well-known Nd2Fe14B magnets with a lower amount of critical elements is required. In this work, we performed density functional theory (DFT) calculations to investigate the influence of partial Nd substitution with more abundant elements (X: Y and Ce) in ThMn12-type (Nd,X)Fe11Ti compounds. In order to have a systematic understanding, the intrinsic magnetic properties such as the saturation magnetization (MS), Curie temperature (TC) and magnetocrystalline anisotropy energy (MAE), are screened starting from binaries RFe12 (R: Y, Ce and Nd). Ti is considered for the thermodynamic stabilization and different concentration of Ti is taken into account for ternaries RFe12−yTiy and quaternaries (Nd,X)Fe12−yTiy (0.5≤y≤1). In addition, the effect of nitrogenation is examined for each considered compounds. Special attention is given for the 4f-electrons treatment and their interaction with 3d-electrons. Each theoretical finding is compared with available experimental data. Since the experimental data is limited in the literature, we could only compare our results for ternaries and obtained reasonable agreement, which encourages us for the quaternary calculations. We have found promising magnetic properties for Nd-lean quaternaries that can be important for technological applications. In the case of (Nd,Y)Fe11Ti compound, |BH|max is found to be 508 kJ/m3, which is a higher value than Sm2Co17 magnets exhibit, and TC is calculated to be 595 K and it is higher than the TC of Nd2Fe14B. Similarly, |BH|max and TC is calculated to be 490 kJ/m3 and 593 K for (Nd,Ce)Fe11Ti magnet, respectively. For both rare-earth-lean quaternaries, our theoretical magnetic hardness factor κ yield to be 1.02, which qualifies them as good candidates for RE-lean permanent magnets.

One-step electrodeposition to fabricate superhydrophobic surfaces on flexible conductive films: Optimization of metallic compounds

Superhydrophobic surfaces were fabricated by a simple one-step electrodeposition technique to deposit three distinct micro/nano hierarchical structures of Ce, Mg, or Cu-based compounds on Ag films on a flexible polymer substrate. Scanning electron microscopy was used to examine the surface morphologies of obtained structures with different deposition. Compared with the bare Ag films, one-step electrodeposition process resulted in superhydrophobicity, including a water contact angle of 159.7° for Ce-modified surfaces, 157.0° for Mg-modified surfaces, and 153.8° for Cu-modified surfaces. Besides, these surfaces showed high thermal stability below 120 ℃, and good flexibility but low electrical conductivity. EDS and XPS results suggest the production of low surface energy materials that formed the superhydrophobic features on the Ag films. Besides, because of the formation of CeO2, Ce-SHS had better superhydrophobicity than Mg-SHS and Cu-SHS. In addition, the potentiodynamic polarization experiments showed that the electrodeposited superhydrophobic surfaces had lower Icorr, higher Ecorr and impedance values in NaCl solution, Na2SO4 solution and Simulated body fluid, and artificial sweat solution compared with the bare silver film, indicating that the electrodeposited protective film has good anti-corrosion properties. These results suggest that the one-step electrodeposition method is a promising strategy to fabricate conducting films with superhydrophobic surfaces for surface protection under various corrosive environments.

Crystal Structures of Ce(IV) Nitrates with Bis(2-pyrrolidone) Linker Molecules Deposited from Aqueous Solutions with Different HNO3 Concentrations

We investigated the molecular and crystal structures of Ce(IV) compounds deposited under different [HNO3] with bis(2-pyrrolidone) linker molecules having a trans-1,4-cyclohexyl bridging moiety (L). As a result, we found that, after loading L, Ce(IV) in HNO3(aq) exclusively provides one of different crystalline phases, (HL)2[Ce(NO3)6] or [Ce2(μ-O)-(NO3)6(L)2]n 2D MOF, depending on [HNO3]. The former has been obtained at [HNO3] = 4.70-9.00 M and is isomorphous with the analogous (HL)2[An(NO3)6] we reported previously. In contrast, the deposition of the latter phase at the lower [HNO3] conditions (1.00-4.30 M) demonstrates that hydrolysis and oxolation of Ce4+ proceed even below pH 0 to provide a [Ce-O-Ce]6+ unit included in this compound. These different Ce(IV) phases are exchangeable with each other under soaking in HNO3(aq), implying that chemical equilibria of dissolution/deposition of these crystalline phases and hydrolysis and oxolation of Ce4+ and its complexation with NO3- occur in parallel. Indeed, such coordination chemistry of Ce(IV) in HNO3(aq) was well corroborated by 17O NMR, Raman, and IR spectroscopy.

Magnetic Toroidal Moment under Partial Magnetic Order in Hexagonal Zigzag-Chain Compound Ce3TiBi5

We theoretically investigate an antiferromagnetic structure in a hexagonal zigzag-chain compound Ce$_3$TiBi$_5$, which shows a linear magnetoelectric effect in metals and an unfamiliar temperature dependence of magnetic susceptibility. We find a partial magnetic order as a coexistence of a nonmagnetic zigzag chain and staggered antiferromagnetic zigzag chains. The latter accompany in-plane magnetic toroidal dipole moments which are responsible for the observed behaviors. We show that magnetic frustration arising from competing exchange interactions plays an important role to realize such a partial magnetic order. Furthermore, we present the important spin-orbit coupling parameters to induce the physical phenomena driven by the magnetic toroidal dipole moment, such as the linear magnetoelectric effect and nonlinear transport.

Structural, magnetic and gamma-ray shielding features of cerium doped Mg2FeTiO6 double perovskite

The Mg2FeTi1-xCexO6 [x=(0, 2, 4, 6, 8, 10)%] ceramics with different Ce concentrations have been prepared by solid-state technique. That compounds were doped with cerium dioxide (CeO2) to develop new material for gamma radiation shielding. The prepared nanomaterials were analyzed to investigate their structural and optical properties by XRD, FTIR, SEM, magnetic properties, and UV techniques. It was determined by the XRPD method that the atomic and molecular structures of Ce-doped compounds were in the tetragonal crystal system and crystallized in the P4/mmm (No: 123) space group. The refinement parameters of the compound Ce doped x = 8% were gof 2.4 and Rf 0.82. The effect of the Ce doping on the magnetization was measured in the magnetic field ranging at ±10 kOe for two temperatures (300 and 10 K) and showed that its Saturation Magnetization (Ms) was increased with the doping increase from 6.2 to 8.1 and from 14.7 to 18.7 for the temperatures 300 and 10 K, respectively. Various radiation shielding parameters for gamma-rays, neutron, and proton were evaluated using Phy-X and SRIM softwares. The linear attenuation coefficient (LAC) increases gradually with adding CeO2 to Mg2FeTiO6 from 54.290 to 92.032 cm−1 at 0.015 MeV. Also, fast neutron removal cross-section (ΣR) rises from 0.077 to 0.115 cm-1 for x = 0 and x = 10%. While the sample x = 10% shows the lowest projectile range for protons. This sample considers the best sample to stop protons. The Analysis demonstrates that the sample with x = 10% shows the highest gamma, proton, and neutron shielding properties nominated it to use in radiation shielding field.

Protection of HDG Steel Using ORMOSIL Coatings Enhanced with CeO2(5-ATDT)- Ceramic Nanocontainers

First, we studied the anticorrosion efficiency of the corrosiveness inhibitors CeO2, 5-amino-1,3,4-thiadiazole- 2-thiol (5-ATDT), Ce(NH4)2(NO3)6 in hot-dip galvanized zinc (HDG) steel. The best protection is shown by the compound Ce(NH4)2(NO3)6 among the three. Second, CeO2 ceramic nanocontainers were prepared, which were loaded with 5-ATDT. Third, organically modified silica (ORMOSIL) coatings were produced on hot-dip galvanized zinc (HDG) steel, which was reinforced with CeO2(5-ATDT) nanocontainers. Finally, the anticorrosion protection of these composites was studied using the Frequency Response Analysis (FRA) method, and it was established to reinforce ORMOSIL with CeO2(5-ATDT); inducing the phenomenon of “self-healing”.

New ternary aluminides Ce0.67Pd2Al5, Ce1.33Pd3Al8, and Ce1.74Pd5.29Al11.71

Polycrystalline samples of novel compounds Ce 0.67 Pd 2 Al 5 , Ce 1.33 Pd 3 Al 8 , and Ce 1.74 Pd 5.29 Al 11.71 were prepared by arc-melting. The crystal structure of the latter compound was determined from the single-crystal X-ray diffraction data to be a disordered variant of the hexagonal Th 2 Ni 17 type [ P 6 3 / mmc , a = 9.1961(5) Å, c = 8.8861(5) Å]. The crystal structures of the other aluminides were examined by powder X-ray diffraction and found to be isotypic with Sc 0.67 Fe 2 Si 5 [ P 6 3 / mmc , a = 4.3385(5) Å, c = 16.5255(15) Å] and Gd 1.33 Pt 3 Al 8 [ R 3 ¯ m , a = 4.37960(10) Å, c = 39.1683(9) Å], respectively. Based on the thermodynamic and electrical resistivity data measured down to 0.4 K in external magnetic fields up to 9 T, the new materials were characterized as metallic Curie-Weiss paramagnets due to fairly stable trivalent Ce ions. In Ce 1.33 Pd 3 Al 8 , an antiferromagnetic ordering was established below T N = 2.3 K, while no long-range magnetic order was found in the other compounds. All three phases exhibit electrical conductivity that is governed by the interplay of Kondo and crystalline electric field interactions, and significantly affected by structural disorder inherent to their crystal lattices. • Novel compounds Ce 0.67 Pd 2 Al 5 , Ce 1.33 Pd 3 Al 8 , and Ce 1.74 Pd 5.29 Al 11.71 were synthesized. • They form with Sc 0.67 Fe 2 Si 5 , Gd 1.33 Pt 3 Al 8 , and Th 2 Ni 17 structure types, respectively. • Electrical transport is strongly affected by structural disorder and Kondo effect.. • They are Curie-Weiss paramagnets; Ce 1.33 Pd 3 Al 8 orders antiferromagnetically at 2.3 K.

Structural 130 K phase transition and emergence of a two-ion Kondo state in Ce2Rh2Ga explored by Ga69,71 nuclear quadrupole resonance

We have studied the microscopic magnetic properties, the nature of the 130-K phase transition, and the ground state in the recently synthesized compound Ce$_2$Rh$_2$Ga by use of $^{69,71}$Ga nuclear quadrupole resonance (NQR). The NQR spectra clearly show an unusual phase transition at $T_t$ $\sim$ 130 K yielding a splitting of the high-temperature single NQR line into two clearly resolved NQR lines, providing evidence for two crystallographically inequivalent Ga sites. The NQR frequencies are in good agreement with fully-relativistic calculations of the band structure. Our NQR results indicate the absence of magnetic or charge order down to 0.3 K. The temperature dependence of the spin-lattice relaxation rate, 1/$T_1$, shows three distinct regimes, with onset temperatures at $T_t$ and 2 K. The temperature-independent 1/$T_1$, observed between $T_t$ and 2 K, crosses over to a Korringa process, 1/$T_1$ $\propto$ $T$, below $\sim$ 2 K, which evidences a rare two-ion Kondo scenario: the system goes into a dense Kondo coherent state at 2.0 and 0.8 K for the two different Ga sites.