Thermophysical properties of SrHfO3 and SrRuO3

Polycrystalline samples of strontium series perovskite type oxides, SrHfO₃ and SrRuO₃ were prepared and the thermophysical properties were measured. The average linear thermal expansion coefficients are 1.13×10⁻⁵ K⁻¹ for SrHfO₃ and 1.03×10⁻⁵ K⁻¹ for SrRuO₃ in the temperature range between 423 and 1073 K. The melting temperatures T_m of SrHfO₃ and SrRuO₃ are 3200 and 2575 K, respectively. The longitudinal and shear sound velocities were measured by an ultrasonic pulse-echo method at room temperature in air, which enables to evaluate the elastic moduli and Debye temperature. The heat capacity was measured by using a differential scanning calorimeter, DSC in high-purity argon atmosphere. The thermal diffusivity was measured by a laser flash method in vacuum. The thermal conductivities of SrHfO₃ and SrRuO₃ at room temperature are 5.20 and 5.97 W m⁻¹ K⁻¹, respectively.     

Cu2Sc2Ge4O13, a novel germanate isotypic with the quasi-1D compound Cu2Fe2Ge4O13 between 100 and 298 K

The germanate compound Cu₂Sc₂Ge₄O₁₃ has been synthesized by solid-state ceramic sintering techniques between 1173 and 1423 K. The structure was solved from single-crystal data by Patterson methods. The title compound is monoclinic, a=12.336(2) Å, b=8.7034(9) Å, c=4.8883(8) Å, β=95.74(2), space group P2₁/m, Z=4. The compound is isotypic with Cu₂Fe₂Ge₄O₁₃, described very recently. The structure consists of crankshaft-like chains of edge-sharing ScO₆ octahedra running parallel to the crystallographic b-axis. These chains are linked laterally by [Cu₂O₆]⁸⁻ dimers forming a sheet of metal-oxygen-polyhedra within the a-b plane. These sheets are separated along the c-axis by [Ge₄O₁₃]¹⁰⁻ units. Cooling to 100 K does not alter the crystallographic symmetry of Cu₂Sc₂Ge₄O₁₃. While the b, c lattice parameter and the unit cell volume show a positive linear thermal expansion (α=6.4(2)×10⁻⁶, 5.0(2)×10⁻⁶ and 8.3(2)×10⁻⁶ K⁻¹ respectively), the a lattice parameter exhibits a negative thermal expansion (α=−3.0(2)×10⁻⁶ K⁻¹) for the complete T-range investigated. This negative thermal expansion of a is mainly due to the increase of the Cu-Cu interatomic distance, which is along the a-axis. Average bond lengths remain almost constant between 100 and 298 K, whereas individual ones partly show both significant shortages and lengthening.     

High-temperature crystal structure and transport properties of the layered cuprates Ln2CuO4, Ln=Pr, Nd and Sm

High-temperature crystal structure of the layered cuprates Ln₂CuO₄, Ln=Pr, Nd and Sm with tetragonal T′-structure was refined using X-ray powder diffraction data. Substantial anisotropy of the thermal expansion behavior was observed in their crystal structures with thermal expansion coefficients (TEC) along a- and c-axis changing from TEC(a)/TEC(c)≈1.37 (Pr) to 0.89 (Nd) and 0.72 (Sm). Temperature dependence of the interatomic distances in Ln₂CuO₄ shows significantly lower expansion rate of the chemical bond between Pr and oxygen atoms (O1) belonging to CuO₂-planes (TEC(Pr-O1)=11.7 ppm K⁻¹) in comparison with other cuprates: TEC (Nd-O1)=15.2 ppm K⁻¹ and TEC (Sm-O1)=15.1 ppm K⁻¹. High-temperature electrical conductivity of Pr₂CuO₄ is the highest one in the whole studied temperature range (298-1173 K): 0.1-108 S/cm for Pr₂CuO₄, 0.07-23 S/cm for Nd₂CuO₄ and 2×10⁻⁴-9 S/cm for Sm₂CuO₄. The trace diffusion coefficient (D_T) of oxygen for Pr₂CuO₄ determined by isotopic exchange depth profile (IEDP) technique using secondary ion mass spectrometry (SIMS) varies in the range 7.2×10⁻¹³ cm²/s (973 K) and 3.8×10⁻¹⁰ cm²/s (1173 K) which are in between those observed for the manganese and cobalt-based perovskites.     

Thermal properties of the pyrochlore, Y2Ti2O7

The thermal conductivity and heat capacity of high-purity single crystals of yttrium titanate, Y₂Ti₂O_7, have been determined over the temperature range 2 K?T?300 K. The experimental heat capacity is in very good agreement with an analysis based on three acoustic modes per unit cell (with the Debye characteristic temperature, θ_D, of ca. 970 K) and an assignment of the remaining 63 optic modes, as well as a correction for C_p−C_v. From the integrated heat capacity data, the enthalpy and entropy relative to absolute zero, are, respectively, H(T=298.15 K)−H₀=34.69 kJ mol⁻¹ and S(T=298.15 K)−S₀=211.2 J K⁻¹ mol⁻¹. The thermal conductivity shows a peak at ca. θ_D/50, characteristic of a highly purified crystal in which the phonon mean free path is about 10 μm in the defect/boundary low-temperature limit. The room-temperature thermal conductivity of Y₂Ti₂O₇ is 2.8 W m⁻¹ K⁻¹, close to the calculated theoretical thermal conductivity, κ_min, for fully coupled phonons at high temperatures.     

The linear thermal expansion and the thermal diffusivity measurements for near-stoichiometric (U, Ce)O2 solid solutions

The thermal diffusivities of near-stoichiometric (U, Ce)O₂ solid solutions containing CeO₂ up to 22 mol% were investigated in the temperature range of 298-1273 K using the laser flash method. Also, linear thermal expansion measurements were performed in the temperature range of 298-1673 K using a thermomechanical analysis. The thermal conductivities were determined by a calculation of the thermal diffusivity, the density and the specific heat. The thermal conductivities of the tested samples could be expressed as a function of the temperature by the phonon conduction equation k = (A + BT)⁻¹. The thermal conductivity decreased gradually with an increasing Ce content. This was attributable to the increasing lattice defect thermal resistance caused by the U⁴⁺, Ce⁴⁺ and O²⁻ ions as phonon scattering centers.     

Thermodynamic properties of BaCeO3 and BaZrO3 at low temperatures

Specific heat capacities (C_p) of polycrystalline samples of BaCeO₃ and BaZrO₃ have been measured from about 1.6 K up to room temperature by means of adiabatic calorimetry. We provide corrected experimental data for the heat capacity of BaCeO₃ in the range T < 10 K and, for the first time, contribute experimental data below 53 K for BaZrO₃. Applying Debye's T³-law for T → 0 K, thermodynamic functions as molar entropy and enthalpy are derived by integration. We obtain C_p = 114.8 (±1.0) J mol⁻¹ K⁻¹, S° = 145.8 (±0.7) J mol⁻¹ K⁻¹ for BaCeO₃ and C_p = 107.0 (±1.0) J mol⁻¹ K⁻¹, S° = 125.5 (±0.6) J mol⁻¹ K⁻¹ for BaZrO₃ at 298.15 K. These results are in overall agreement with previously reported studies but slightly deviating, in both cases. Evaluations of C_p(T) yield Debye temperatures and identify deviations from the simple Debye-theory due to extra vibrational modes as well as anharmonicity. The anharmonicity turns out to be more pronounced at elevated temperatures for BaCeO₃. The characteristic Debye temperatures determined at T = 0 K are Θ₀ = 365 (±6) K for BaCeO₃ and Θ₀ = 402 (±9) K for BaZrO₃.     

Anisotropic thermal expansion and hydrogen bonding behavior of portlandite: A high-temperature neutron diffraction study

The structure of deuterated portlandite, Ca(OD)₂, was investigated using time-of-flight neutron diffraction in the temperature range 308-643 K. Rietveld analysis reveals that with increasing temperature, the c dimension expands at a rate ∼4.5 times larger than that for a. This anisotropy of thermal expansion is due to rapid increase in the interlayer thickness along c with increasing temperature. Fitting of the measured cell volumes yields a coefficient of thermal expansion, α=α₀+α₁T, where α₀=5.966×10⁻⁵ K⁻¹ and α₁=3.333×10⁻⁸ K⁻². On heating, hydrogen-mediated interatomic interactions within the interlayer become weakened, as reflected by increases in the interlayer D?O and D?D distances with increasing temperature. Correspondingly, the three equivalent sites over which D is disordered become further apart, suggesting a more delocalized configuration of D at high temperatures.     

Mixed conductivity and Mössbauer spectra of (La0.5Sr0.5)1−xFe1−yAlyO3−δ (x=0-0.05, y=0-0.30)

Aluminum incorporation in the rhombohedrally distorted perovskite lattice of (La_0.5Sr_0.5)_1−xFe_1−yAl_yO_3−δ (x=0-0.05, y=0-0.30) decreases the unit cell volume and partial ionic and p-type electronic conductivities, while the oxygen nonstoichiometry and thermal expansion at 900-1200 K increase on doping. The creation of A-site cation vacancies has an opposite effect on the transport properties of Al-substituted ceramics. The maximum A-site deficiency tolerated by the (La,Sr)(Fe,Al)O_3−δ structure is however limited, close to 3-4%. The Mössbauer spectroscopy revealed progressive localization of electron holes and a mixed charge-compensation mechanism, which results in higher average oxidation state of iron when Al³⁺ concentration increases. The average thermal expansion coefficients of (La_0.5Sr_0.5)_1−xFe_1−yAl_yO_3−δ are (12.2-13.0)×10⁻⁶ K⁻¹ at 300-900 K and (20.1-30.0)×10⁻⁶ K⁻¹ at 900-1200 K in air. The steady-state oxygen permeability (OP) of dense Al-containing membranes is determined mainly by the bulk ionic conductivity. The ion transference numbers at 973-1223 K in air, calculated from the oxygen permeation and faradaic efficiency (FE) data, vary in the range 1×10⁻⁴-3×10⁻³, increasing with temperature.     

Structural, magnetic and electronic properties of LaNi0.5Fe0.5O3 in the temperature range 5-1000 K

The structure, magnetism, transport and thermal expansion of the perovskite oxide LaNi_0.5Fe_0.5O₃ were studied over a wide range of temperatures. Neutron time-of-flight data have shown that this compound undergoes a first-order phase transition between ∼275 and ∼310 K. The structure transforms from orthorhombic (Pbnm) at low temperatures to rhombohedral (R3¯c) above room temperature. This phase transition is the cause for the previously observed co-existence of phases at room temperature. The main structural modification associated with the phase transition is the change of tilting pattern of the octahedra from a⁺b⁻b⁻ at low temperatures to a⁻a⁻a⁻ at higher. Magnetic data strongly suggests that a spin-glass magnetic state exists in the sample below 83 K consistent with the absence of magnetic ordering peaks in the neutron data collected at 30 K. At high temperatures the sample behaves as a small polaron electronic conductor with two regions of slightly different activation energies of 0.07 and 0.05 eV above and below 553 K, respectively. The dilatometric data show an average thermal expansion coefficient of 14.7×10⁻⁶ K⁻¹ which makes this material compatible with frequently used electrolytes in solid oxide fuel cells.     

X-ray diffraction study on the thermal expansion behavior of cellulose Iβ and its high-temperature phase

Oriented films of cellulose prepared from algal cellulose were hydrothermally treated to convert them into highly crystalline cellulose Iβ. The lateral thermal expansion behavior of the prepared cellulose Iβ films was investigated using X-ray diffraction at temperatures from 20 to 300 °C. Cellulose Iβ was transformed into the high-temperature phase when the temperature was above 230 °C, allowing the lateral thermal expansion coefficient of cellulose Iβ and its high-temperature phase to be measured. For cellulose Iβ, the thermal expansion coefficients (TECs) of the a- and b-axes were α_a = 9.8 × 10⁻⁵ °C⁻¹ and α_b = 1.2 × 10⁻⁵ °C⁻¹, respectively. This anisotropic thermal expansion behavior in the lateral direction is ascribed to the crystal structure and to the hydrogen-bonding system of cellulose Iβ. For the high-temperature phase, the anisotropy was more conspicuous, and the TECs of the a- and b-axes were α_a = 19.8 × 10⁻⁵ °C⁻¹ and α_b = −1.6 × 10⁻⁵ °C⁻¹, respectively. Synchrotron X-ray fiber diffraction diagrams of the high-temperature phase were also recorded at 250 °C. The cellulose high-temperature phase is composed of a two-chain monoclinic unit cell, a = 0.819 nm, b = 0.818 nm, c (fiber repeat) = 1.037 nm, and γ = 96.4°, with space group = P2₁. The volume of this cell is 4.6% larger than that of cellulose Iβ at 30 °C.     

Preparation, crystal structure and thermal expansion of a new bismuth barium borate, BaBi2B4O10

Single crystals of a new compound, BaBi₂B₄O₁₀ were grown by cooling a melt with the stoichiometric composition. The crystal structure of the compound has been solved by direct methods and refined to R₁=0.049 (wR=0.113) on the basis of 1813 unique observed reflections (|F_o|>4σ|F_o|). It is monoclinic, space group P2₁/c, a=10.150(2), b=6. 362(1), c=12.485(2) Å, β=102.87(1)^o, V=786.0(2) Å³, Z=4. The structure is based upon anionic thick layers that are parallel to (001). The layers can be described as built from alternating novel borate [B₄O₁₀]⁸⁻_∞ chains and bismuthate [Bi₂O₅]⁴⁻_∞ chains extended along b-axis. The borate chains are composed of [B₃O₈]⁷⁻ triborate groups of three tetrahedra and single triangles with a [BO₂]⁻ radical. The borate chains are interleaved along the c-axis with rows of the Ba²⁺ cations so that the Ba atoms are located within the layers. The layers are connected by two nonequivalent Ba-O bonds as well as by two equivalent Bi-O bonds with bond valences in the range of 0.2-0.3 v.u.Thermal expansion of BaBi₂B₄O₁₀ studied by high-temperature X-ray powder diffraction in the temperature range of 20-700 °C (temperature step 30-35 °C) is highly anisotropic. While the b and c unit-cell parameters increase almost linearly on heating, temperature dependencies of a parameter and β monoclinic angle show nonlinear behavior. As a result, on heating orientation of thermal expansion tensor changes, and bulk thermal expansion increases from 20×10⁻⁶ °C⁻¹ at the first heating stage up to 57×10⁻⁶ °C⁻¹ at 700 °C that can be attributed to the increase of thermal mobility of heavy Bi³⁺ and Ba²⁺ cations.     

p-Type thermoelectric properties of the oxygen-deficient perovskite Ca2Fe2O5 in the brownmillerite structure

Brownmillerite calcium ferrite was synthesized in air at 1573 K and thermoelectric properties (direct current electrical conductivity σ, Seebeck coefficient α, thermal conductivity κ, thermal expansion α_L) were measured from 373 to 1050 K in air. Seebeck coefficient was positive over all temperatures indicating conduction by holes, and electrical properties were continuous through the Pnma-Imma phase transition. Based on the thermopower and conductivity activation energies as well as estimated mobility, polaron hopping conduction was found to dominate charge transport. The low electrical conductivity, <1 S/cm, limits the power factor (α²σ), and thus the figure of merit for thermoelectric applications. The thermal conductivity values of ∼2 W/mK and their similarity to Ruddlesden-Popper phase implies the potential of the alternating tetrahedral and octahedral layers to limit phonon propagation through brownmillerite structures. Bulk linear coefficient of thermal expansion (∼14×10⁻⁶ K⁻¹) was calculated from volume data based on high-temperature in situ X-ray powder diffraction, and shows the greatest expansion perpendicular to the alternating layers.     

Thermoelectric properties of polycrystalline La1−xSrxCoO3

Thermoelectric properties of polycrystalline La_1−xSr_xCoO₃, where Sr²⁺ is substituted in La³⁺ site in perovskite-type LaCoO₃, have been investigated. Sr-doping increases the electrical conductivity (σ) of La_1−xSr_xCoO₃, and also decreases the Seebeck coefficient (S) for 0.01?x?0.40. A Hall coefficient measurement reveals that the increase in electrical conductivity arises from increases in both carrier concentration and the Hall mobility. The decrease in the Seebeck coefficient is caused by a decrease in carrier effective mass as well as increase in carrier concentration. The highest power factor (σS²) is 3.7×10⁻⁴ W m⁻¹ K⁻² at 250 K for x=0.10. The thermal conductivity (κ) is about 2 W m⁻¹ K⁻¹ at 300 K for 0?x?0.04, and increases for x?0.05 because of an increase in heat transport by conductive carrier. The thermoelectric properties of La_1−xSr_xCoO₃ are improved by Sr-doping, and the figure of merit (Z=σS² κ⁻¹) reaches 1.6×10⁻⁴ K⁻¹ for x=0.06 at 300 K (ZT=0.048). For heavily Sr-doped samples, the thermoelectric properties diminish mainly because of the decrease in the Seebeck coefficient and the increase in thermal conductivity.     

Structure and high-temperature thermoelectric properties of SrAl2Si2

Single crystals of SrAl₂Si₂ were synthesized by reaction of the elements in an aluminum flux at 1000 °C. SrAl₂Si₂ is isostructural to CaAl₂Si₂ and crystallizes in the hexagonal space group P-3m1 (90 K, a=4.1834 (2), c=7.4104 (2) Å, Z=1, R1=0.0156, wR2=0.0308). Thermal analysis shows that the compound melts at ∼1020 °C. Low-temperature resistivity on single crystals along the c-axis shows metallic behavior with room temperature resistivity value of ∼7.5 mΩ cm. High-temperature Seebeck, resistivity, and thermal conductivity measurements were made on hot-pressed pellets. The Seebeck coefficient shows negative values in entire temperature range decreasing from ∼−78 μV K⁻¹ at room temperature to −34 μV K⁻¹ at 1173 K. Seebeck coefficients are negative indicating n-type behavior; however, the temperature dependence is consistent with contribution from minority p-type carriers as well. The lattice contribution to the thermal conductivity is higher than for clathrate structures containing Al and Si, approximately 50 mW cm⁻¹ K, and contributes to the overall low zT for this compound.     

Synthesis, crystal structure and thermal behavior of Sr3B2SiO8 borosilicate

Single crystals of Sr₃B₂SiO₈ were obtained by solid-state reaction of stoichiometric mixture at 1200 °C. The crystal structure of the compound has been solved by direct methods and refined to R1=0.064 (wR=0.133). It is orthorhombic, Pnma, a=12.361(4), b=3.927(1), c=5.419(1) Å, V=263.05(11) Å³. The structure contains zigzag pseudo-chains running along the b axis and built up from corner sharing (Si,B)−O polyhedra. Boron and silicon are statistically distributed over one site with their coordination strongly disordered. Sr atoms are located between the chains providing three-dimensional linkage of the structure.The formation of Sr₃B₂SiO₈ has been studied using annealing series in air at 900-1200 °C. According powder XRD, the probe contains pure Sr₃B₂SiO₈ over 1100 °C. The compound is not stable below 900 °C. In the pseudobinary Sr₂B₂O₅-Sr₃B₂SiO₈ system a new series of solid solutions Sr_3−xB₂Si_1−xO_8−3x (x=0-0.9) have been crystallized from melt. The thermal behavior of Sr₃B₂SiO₈ was investigated using powder high-temperature X-ray diffraction (HTXRD) in the temperature range 20-900 °C. The anisotropic character of thermal expansion has been observed: α_a= −1.3, α_b=23.5, α_c=13.9, and α_V=36.1×10⁻⁶ °C⁻¹ (25 °C); α_a= −1.3, α_b=23.2, α_c=5.2, and α_V=27.1×10⁻⁶ °C⁻¹ (650 °C). Maximal thermal expansion of the structure along of the chain direction [0 1 0] is caused by the partial straightening of chain zigzag. Hinge mechanism of thermal expansion is discussed.     

Cu22Bi12S21Cl16—A mixed conductor with fast one-dimensional copper(I) ion transport

Melting reactions of Cu, CuCl, S, and Bi₂S₃ yield black, shiny needles of Cu₂₂₍₁₎Bi₁₂S₂₁₍₁₎Cl₁₆₍₁₎. The compound decomposes peritectically at 649(5) K. Oxidation state +I of the copper atoms is supported by Cu-K-XANES. The compound crystallizes in the hexagonal space group P6/m with a=2116.7(7) pm and c=395.17(5) pm. Seven anions coordinate each of the two independent bismuth cations in the shape of mono-capped trigonal prisms. These polyhedra share edges and faces to form trigonal and hexagonal tubes running along [0 0 1]. The hexagonal tubes are centered by chloride ions, which are surrounded by disordered copper cations. The majority of copper cations are distributed over numerous sites between the tubes. The Joint Probability Density Function (JPDF) reveals a continuous pathway along [0 0 1]. The high mobility of the copper cations along [0 0 1] was demonstrated by impedance spectroscopy and DC polarization measurements on single crystals. The ionic conductivity at 450 K is about σ_ion=0.06 S cm⁻¹, and the activation energy for Cu⁺ ion conduction is E_a=0.44 eV. The chemical diffusion coefficient of copper is in the order of D_cu^δ=10¹⁹ cm⁻³ at 420 K. The electronic band gap (p-type conductor) was determined as E_g=0.06 eV. At room temperature the thermal conductivity of a pressed pellet is about κ=0.3 W K⁻¹ m⁻¹ and the Seebeck coefficient is S=43 μV K⁻¹.     

Structural changes accompanying negative thermal expansion in Zr2(MoO4)(PO4)2

Zr₂(MoO₄)(PO₄)₂ is orthorhombic (Sc₂W₃O₁₂ structure) from 9 to at least 400 K, and shows anisotropic volume negative thermal expansion (α_a=−8.35(4)×10⁻⁶ K⁻¹; α_b=3.25(3)×10⁻⁶ K⁻¹; α_c=−8.27(5)×10⁻⁶ K⁻¹ in the range 122-400 K) similar in magnitude to A₂M₃O₁₂ (M—Mo or W) with large A³⁺. The contraction on heating is associated with a pattern of Zr-O-Mo/P bond angle changes that is somewhat similar, but not the same as that for Sc₂W₃O₁₂. On heating, the most pronounced reductions in the separation between the crystallographic positions of neighboring Zr and P are not associated with significant reductions in the corresponding Zr-O-P crystallographic bond angles, in contrast to what was seen for Sc₂W₃O₁₂.     

The study of Bi3B5O12: synthesis, crystal structure and thermal expansion of oxoborate Bi3B5O12

The paper presents a new data on the crystal structure, thermal expansion and IR spectra of Bi₃B₅O₁₂. The Bi₃B₅O₁₂ single crystals were grown from the melt of the same stoichiometry by Czochralski technique. The crystal structure of Bi₃B₅O₁₂ was refined in anisotropic approximation using single-crystal X-ray diffraction data. It is orthorhombic, Pnma, a=6.530(4), b=7.726(5), c=18.578(5) Å, V=937.2(5) Å³, Z=4, R=3.45%. Bi³⁺ atoms have irregular coordination polyhedra, Bi(1)O₆ (d(B-O)=2.09-2.75 Å) and Bi(2)O₇ (d(B-O)=2.108-2.804 Å). Taking into account the shortest bonds only, these polyhedra are considered here as trigonal Bi(1)O₃ (2.09-2.20 Å) and tetragonal Bi(2)O₄ (2.108-2.331 Å) irregular pyramids with Bi atoms in the tops of both pyramids. The BiO₄ polyhedra form zigzag chains along b-axis. These chains alternate with isolated anions [B₂^IVB₃^IIIO₁₁]⁷⁻ through the common oxygen atoms to form thick layers extended in ab plane. A perfect cleavage of the compound corresponds to these layers and an imperfect one is parallel to the Bi-O chains. The Bi₃B₅O₁₂ thermal expansion is sharply anisotropic (α₁₁≈α₂₂=12, α₃₃=3×10⁻⁶ °C⁻¹) likely due to a straightening of the flexible zigzag chains along b-axis and decreasing of their zigzag along c-axis. Thus the properties like cleavage and thermal expansion correlate to these chains.     

Studies on lattice thermal expansion and XPS of ThO2NdO1.5 solid solutions

The lattice parameter changes with respect to temperature (T) have been measured by high temperature X-ray diffraction (HTXRD) technique for ThO₂NdO_1.5 solid solutions containing 23.8 and 42.5 mol% NdO_1.5 in the temperature range from 298 to 2000 K. The temperature versus lattice parameter data have been made use of in calculating the lattice thermal expansivity. The values of thermal expansion of the solid solutions were found to be increased with increase in neodymium oxide content and temperature. The mean linear thermal expansion coefficients in this temperature range for ThO₂NdO_1.5 solid solutions are 12.28 × 10⁻⁶ and 12.90 × 10⁻⁶ K⁻¹, respectively. The binding energies of Th 4f_7/2 and Nd 3d_5/2 energy levels of the solid solutions containing 13.1, 23.8, 31.9, 37.2 and 42.5 mol% NdO_1.5 and two-phase mixtures containing 47.6 and 51.8 mol% NdO_1.5 were experimentally determined by X-ray photoelectron spectroscopy (XPS).