Improved electrical properties of Co-doped 0.92NBT–0.04KBT–0.04BT lead-free ceramics

The (1???2x)NBT–xKBT–xBT ternary piezoelectric system has been extensively studied in recent years. However, its electrical performance is far inferior to lead-based counterparts, and could not meet the requirements for practical applications. In this contribution, the 0.92NBT–0.04KBT–0.04BT (abbreviated as NKBT4) ceramics were prepared by traditional solid-state method. The effects of doped cobalt content on the structure and electrical performance of NKBT4 ceramics were studied systematically. The content of Co₂O₃ affects the average grain size, maximum dielectric constant, piezoelectric properties and the ferroelectric responses of the ceramics. It was found that the introduction of cobalt did not affect the phase structure of the ceramics, but is beneficial for the improvement of the dielectric and piezoelectric properties. When x?=?0.2, the piezoelectric coefficient (d₃₃) is around 130 pC/N, which is greatly improved compared to pure NKBT4 ceramics. Besides, a relatively high dielectric constant (ε_r?=?1150) was obtained at the same composition. This work paves a new way for the further development of high performance lead-free piezoelectric ceramics.     

Enhanced magnetoelectric coupling in La-modified Bi<Subscript>5</Subscript>Co<Subscript>0.5</Subscript>Fe<Subscript>0.5</Subscript>Ti<Subscript>3</Subscript>O<Subscript>15</Subscript> multiferroic ceramics

Multiferroic properties of La-modified four-layered perovskite Bi_5?x La _x Fe_0.5Co_0.5Ti₃O₁₅ (0 ≤ x ≤ 1) ceramics were investigated, by analyzing the magnetodielectric effect, magneto-polarization response and magnetoelectric conversion. X-ray diffraction indicated the formation of pure Aurivillius ceramics, and Raman spectroscopy revealed the Bi ions displacement and the crystal structure variation. The enhancement of ferromagnetic and ferroelectric properties was observed in Bi_5?x La _x Fe_0.5Co_0.5Ti₃O₁₅ after La modification. The evidence for enhanced ME coupling was determined by magnetic field-induced marked variations in the dielectric constant and polarization. A maximum ME coefficient of 1.15 mV/cm·Oe was achieved in Bi_4.25La_0.75Fe_0.5Co_0.5Ti₃O₁₅ ceramic, which provides the possible promise for novel magnetoelectric device application.     

Controllable preparation of large-area arrays of Al-substituted CoCuNi ferrite rods with improvement of saturation magnetization and initial permeability

Co_0.5Cu_0.3Ni_0.2Al _x Fe_2?x O₄ (x = 0, 0.07, 0.14, and 0.21) rods of large-area arrays are synthesized by a solvothermal method, followed by calcination in air. The samples are characterized by powder X-ray diffraction, FT-IR spectra, scanning electron microscope, and vibrating sample magnetometer. The effect of diamagnetic Al³⁺ ion substitution and calcination temperature on the structure, morphology, and magnetic properties of Co_0.5Cu_0.3Ni_0.2Al _x Fe_2?x O₄ has been investigated. The results indicate that high-crystallized cubic Co_0.5Cu_0.3Ni_0.2Al _x Fe_2?x O₄ rods of large-area arrays are obtained when the precursors are calcined at 750 °C in air for 3 h. The crystallite size of Co_0.5Cu_0.3Ni_0.2Al _x Fe_2?x O₄ increases with the increase in Al³⁺ content, attributed to the decrease in lattice strain in Co_0.5Cu_0.3Ni_0.2Al _x Fe_2?x O₄ with the increase in Al³⁺ content. The lattice parameters of Co_0.5Cu_0.3Ni_0.2Al _x Fe_2?x O₄ slightly increase with the increase in Al³⁺ content. This is due to the transformation from cubic NiFe₂O₄ phase to cubic CoFe₂O₄ phase after doping Al³⁺ ion. Al³⁺ substitution can improve the magnetic properties of Co_0.5Cu_0.3Ni_0.2Al _x Fe_2?x O₄. Co_0.5Cu_0.3Ni_0.2Al_0.14Fe_1.86O₄, calcined at 950 °C, has the highest specific saturation magnetization (86.36 ± 2.25 emu/g) and magnetic moment (3.586 ± 0.093 μ _B ). Co_0.5Cu_0.3Ni_0.2Al_0.21Fe_1.79O₄, calcined at 950 °C, has the highest initial permeability (17.216 ± 0.448). The results are explained by Neel’s two sublattices.     

Structural Formation and Improved Performances of Chemically Synthesized Composition-Controlled Micron-Sized Fe100−x Co x Particles

Micron-sized composition-controlled Fe_100?x Co _x (20 < x < 75) alloy particles with high purity have been prepared by an optimized reduction reaction. The influence of Co content on the alloying process, structures, and magnetic properties of the products has been studied. The as-synthesized Fe_{100 ?x} Co _x with x < 65 exhibit a single bcc crystal structure. A bcc-FeCo/fcc-Co composite structure can be formed in the Fe_100?x Co _x products with x > 65. Very slight surface oxidation is observed in all the products. The high purity and single bcc-FeCo phase for the well-alloyed Fe_{100 ?x} Co _x particles with x < 65 lead to their high saturation magnetization of 182–220 A m² kg^?1. All the well-alloyed Fe_{100 ?x} Co _x show nearly spherical morphologies with an average particle size of 2–8 μm, which results in their good compactibility with a high compacted density of about 7.4–7.6 g cm^?3. The simple preparation and improved performances for these chemically synthesized composition-controlled FeCo particles show their great potential for applications in near-net-shaped and complex-shaped FeCo-based soft magnetic composite devices.     

Influence of isovalent and heterovalent substitution for Bi<Superscript>3+</Superscript> and Fe<Superscript>3+</Superscript> on the properties of Bi<Subscript>2</Subscript>Fe<Subscript>4</Subscript>O<Subscript>9</Subscript>-based solid solutions

Bi_2–хLa_хFe₄O₉ and Bi₂Fe_4–2xTi_xCo_xO₉ ferrites have been prepared by solid-state reactions at a temperature of 1073 K. X-ray diffraction data indicate that, in the Bi_2–хLa_хFe₄O₉ system, the limiting degree of La³⁺ substitution for Bi³⁺ ions in Bi₂Fe₄O₉ does not exceed 0.05 and that the limiting degree of substitution in the Bi₂Fe_4–2xTi_xCo_xO₉ system lies in the range 0.05 < x < 0.1. The specific magnetization and specific magnetic susceptibility of the samples have been measured at temperatures from 5 to 300 K in a magnetic field of 0.86 T. The field dependences of magnetization obtained for the Bi_2–хLa_хFe₄O₉ and Bi₂Fe_4–2xTi_xCo_xO₉ ferrites at temperatures of 300 and 5 K demonstrate that partial isovalent substitution of La³⁺ for Bi³⁺ ions in Bi₂Fe₄O₉ and heterovalent substitution of Ti⁴⁺ and Co²⁺ ions for two Fe³⁺ ions leads to partial breakdown of the antiferromagnetic state and nucleation of a ferromagnetic state.     

Effects of Nb doping on the microstructure,ferroelectric and piezoelectric properties of 0.7BiFeO<Subscript>3</Subscript>–0.3BaTiO<Subscript>3</Subscript> lead-free ceramics

Donor-doped lead-free Bi_0.7Ba_0.3(Fe_0.7Ti_0.3)_1?x Nb_0.66x O₃ + 1 mol% MnO₂ ceramics were prepared by a conventional oxide-mixed method and the effects of Nb-doping on microstructure, piezoelectric and ferroelectric properties of the ceramics were investigated. All the ceramics exhibit a pure perovskite structure with rhombohedral symmetry. The grain growth of the ceramics is inhibited after the addition of Nb doping. High electric insulation (R = 10⁹–10¹⁰ Ω?cm) and the poor piezoelectric performance and weak ferroelectricity are observed after the addition of Nb₂O₅ in the ceramics. Different from the donor effect of Pb-based perovskite ceramics, the introduction of Nb into 0.7BiFeO₃–0.3BaTiO₃ degrades the piezoelectricity and ferroelectricity of the ceramics. The Bi_0.7Ba_0.3(Fe_0.7Ti_0.3)_1?x Nb_0.66x O₃ + 1 mol% MnO₂ ceramic with x = 0 exhibits the optimum piezoelectric properties with d ₃₃ = 133 pN C^?1 and k _p = 0.29 and high Curie temperature (T_C = 603^°C).     

Lattice Energy Determination for Polycrystalline Oxide Ceramics and Single-Crystalline Counterparts

The compositional dependence of lattice energies for polycrystalline specimens of spinel ferrite systems, Zn _x Co_1?x Fe₂ O ₄ (x = 0.0–0.6); slowly cooled and quenched systems of CuAl _x Fe_2?x O ₄ (x = 0.0–0.6); high-energy ball milled mixed ferrite composition, Ni_0.5Zn_0.5Fe₂ O ₄ (0–9 h); garnet system, Y_3?x Fe_{5 + x} O ₁₂ (x = 0.0–0.5); manganite perovskite system, La_1?x Ca _x MnO₃ (x = 0.0–1.0); and superconducting systems, Bi_1.7?x Pb_0.3Al _x Sr₂Ca₂Cu₃ O ₁₀ (x = 0.0–0.3), Bi_1.7?x Pb_0.3Ga _x Sr₂CaCu₂ O ₈ (x = 0.0–0.3), and Bi₂Sr₂CaCu₂ O ₈+0??5 % Ag ⁺ addition has been evaluated, making use of mean sound velocity data and employing Kudriavtsev’s approach. It is found that for all the systems, lattice energy decreases, and it is explained based on the change in structural and microstructural parameters as a function of substitution. The lattice energies for single-crystalline counterparts have been computed using four different estimation models based on Kapustinskii method, molecular volume and X-ray density, connectivity indices, and chemical hardness. The observed difference between the two has been discussed in the light of grain and grain boundary contributions and presence of pores and microcracks in polycrystalline materials. A simple model suggested for lattice energy determination for complex oxide compositions based on the oxide additivity rule was found to be quite satisfactory.     

Phase equilibria and crystal structures of phases in the La-Fe-Ni-O system at 1370 K in air

The phase equilibria in the La-Fe-Ni-O system have been studied at 1370 K in air, and the La-Fe-Ni-O phase diagram at constant temperature and pressure has been constructed. Based on x-ray diffraction results for samples prepared by standard solid-state reactions and via citrate and nitrate routes, the following solid solutions have been shown to exist at 1370 K in air: LaFe_{1 ? x} Ni _x O_{3 ? δ} (0 < x ≤ 0.4, sp. gr. Pbnm; 0.6 ≤ x ≤ 0.8, sp. gr. R-3 c), La₄(Ni_{1 ? y} Fe _y )₃O_{10 ? δ} (0 < y ≤ 0.3), La₃(Ni_{1 ? z} Fe _z )₂O_{7 ? δ} (0 < z ≤ 0.05), La₂Ni_{1 ? v} Fe _v O_{4 + δ} (0 < v ≤ 0.05), Ni_kFe_{3 ? k} O₄ (0.81 ≤ k ≤ 1.05), Ni_{1 ? m} Fe _m O (0 < m ≤ 0.05), and Fe_{2 ? p} Ni _p O₃ (0 < p ≤ 0.04). The lattice constants and structural parameters of single-phase samples have been refined by the Rietveld profile analysis method.     

Phase Distribution and Magnetic Properties of Mechanically Alloyed Hard/Soft Ferrite Nanocomposites

Improvement in the magnetic properties of hard/ soft ferrite nanocomposites was studied by varying the composition of the soft phase in SrFe₁₂O₁₉/Ni_0.5Zn_0.5Fe₂O₄ nanocomposites. The SrFe₁₂O₁₉/Ni_0.5Zn_0.5Fe₂O₄ nanocomposites were prepared using the mechanical alloying method. The samples were prepared by varying the amount of the soft phase from 10 to 50 wt% while the amount of the hard phase remained 100 wt% in the ferrite nanocomposites. X-ray diffraction (XRD), a vibrating sample magnetometer (VSM), and a transmission electron microscope (TEM) were used to characterize the samples. From the result, it was found that the nanocomposite magnet with 10 wt% of soft phase content had the highest remanence ratio, M _r / M _s , which was 0.61, while the values of the coercivity, H _c , and magnetization, M _s , measured were 4482.4 G and 9.71 emu/g, respectively, and the average particle size of the ferrite nanocomposites was < 50 nm for all the samples. It was also shown that H _c decreased as the weight percent of the soft ferrite increased, which resulted from the dipolar interaction that occurred in the ferrite nanocomposites, showing the effect of phase distribution on the magnetic properties.     

Critical Behavior of La<Subscript>0.67</Subscript>Ba<Subscript>0.33</Subscript>Mn<Subscript>0.95</Subscript>Fe<Subscript>0.05</Subscript>O<Subscript>3</Subscript> Manganite

The critical behavior of perovskite manganite La_0.67Ba_0.33Mn_0.95Fe_0.05O₃ at the ferromagnetic–paramagnetic has been analyzed. The results show that the sample exhibited the second-order magnetic phase transition. The estimated critical exponents derived from the magnetic data using various such as modified d’Arrott plot Kouvel–Fisher method and critical magnetization M(T _C, H). The critical exponents values for the La_0.67Ba_0.33Mn_0.95Fe_0.05O₃ are close to those expected from the mean field model β = 0.504 ± 0.01 with T _C = 275661 ± 0.447 (from the temperature dependence of the spontaneous magnetization below T _C ), γ = 1.013 ± 0.017 with T _C = 276132 ± 0.452 (from the temperature dependence of the inverse initial susceptibility above T _C ), and δ = 3.0403 ± 0.0003. Moreover, the critical exponents also obey the single scaling equation of M(H, ε) = |ε| ^β f _±(H/|ε| ^β+γ ).     

Error tolerance for the recognition of faulty strings in a regulated grammar using fuzzy sets

To overcome the limitations of context-free and context-sensitive grammars, regulated grammars have been proposed. In this paper, an algorithm is proposed for the recognition of faulty strings in regulated grammar. Furthermore, depending on the errors and certainty, it is decided whether the string belongs to the language or not based on string membership value. The time complexity of the proposed algorithm is O(|G _R ² |·|w|), where |G_R| represents the number of production rules and |w| is the length of the input string, w. The reader is provided with numerical examples by applying the algorithm to regularly controlled and matrix grammar. Finally, the proposed algorithm is applied in the Hindi language for the recognition of faulty strings in regulated grammar as a real-life application.     

Sintering behavior,phase structure and electric properties of KNNTS-BKNZ ceramics with excessive alkali metals

We investigated the effect of excessive alkali metals on sintering character, phase structure, dielectric, piezoelectric and ferroelectric properties in KNN-based ceramics thoroughly. The 0.96(K_0.48Na_0.52)_1+xNb_0.93Sb_0.02Ta_0.05O₃–0.04Bi_0.5(K_0.12Na_0.88)_0.5ZrO₃ [(KN) _x NTS-BKNZ] lead-free piezoelectric ceramics were prepared by conventional solid-state reaction method. The sintering temperature of (KN) _x NTS-BKNZ ceramics increases gradually while the sintering temperature zone becomes narrow with the increasing x value. For the composition of x?>?0.03, the grains could not grow in all sintering temperature. The coexistence system of rhombohedral and tetragonal phases has been found in (KN) _x NTS-BKNZ ceramics and the T_R?T, T_C, d₃₃, and ε_r show a upward tendency with the increasing x when 0?≤?x?≤?0.03. The maximal piezoelectric coefficient d₃₃ of 415 pC/N was obtained at x?=?0.03. In addition, these ceramics presented good temperature stability. This study exhibits that excessive alkali metals influence sintering character and electrical properties on KNN ceramics deeply. It was believed that this work would be helpful for further understanding the effect of excessive alkali metals on sintering behavior and electric properties in KNN-based ceramics.     

Structure and electrical properties of MnO doped (Ba<Subscript>0.96</Subscript>Ca<Subscript>0.04</Subscript>)(Ti<Subscript>0.92</Subscript>Sn<Subscript>0.08</Subscript>)O<Subscript>3</Subscript> lead free ceramics

In this work, (Ba_0.96Ca_0.04)(Ti_0.92Sn_0.08)O₃–xmol MnO (BCTS–xMn) lead-free piezoelectric ceramics were fabricated by the conventional solid-state technique. The composition dependence (0 ≤ x ≤ 3.0 %) of the microstructure, phase structure, and electrical properties was systematically investigated. An O–T phase structure was obtained in all ceramics, and the sintering behavior of the BCTS ceramics was gradually improved by doping MnO content. In addition, the relationship between poling temperature and piezoelectric activity was discussed. The ceramics with x = 1.5 % sintering at temperature of 1330 °C demonstrated an optimum electrical behavior: d ₃₃ ~ 475 pC/N, k _p ~ 50 %, ε _r ~ 4060, tanδ ~ 0.4 %, P _r ~ 10.3 μC/cm², E _c ~ 1.35 kV/mm, T _C ~ 82 °C, strain ~0.114 % and \(d_{33}^{*}\) ~ 525 pm/V. As a result, we achieved a preferable electric performance in BaTiO₃-based ceramics with lower sintering temperature, suggesting that the BCTS–xMn material system is a promising candidate for lead-free piezoelectric ceramics.     

Effects of Ge<Superscript>4+</Superscript> acceptor dopant on sintering and electrical properties of (K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)NbO<Subscript>3</Subscript> lead-free piezoceramics

Lead-free (K_0.5Na_0.5)(Nb_1-xGe _x )O₃ (KNN-xGe, where x = 0-0.01) piezoelectric ceramics were prepared by conventional ceramic processing. The effects of Ge⁴⁺ cation doping on the phase compositions, microstructure and electrical properties of KNN ceramics were studied. SEM images show that Ge⁴⁺ cation doping improved the sintering and promoted the grain growth of the KNN ceramics. Dielectric and ferroelectric measurements proved that Ge⁴⁺ cations substituted Nb⁵⁺ ions as acceptors, and the Curie temperature (T_C) shows an almost linear decrease with increasing the Ge⁴⁺ content. Combining this result with microstructure observations and electrical measurements, it is concluded that the optimal sintering temperature for KNN-xGe ceramics was 1020°C. Ge⁴⁺ doping less than 0.4 mol.%can improve the compositional homogeneity and piezoelectric properties of KNN ceramics. The KNN-xGe ceramics with x = 0.2% exhibited the best piezoelectric properties: piezoelectric constant d₃₃ = 120 pC/N, planar electromechanical coupling coefficient k_p = 34.7%, mechanical quality factor Q_m = 130, and tanδ = 3.6%.     

Synthesis,structure, and magnetic properties of rare-earth-doped Ni<Subscript>0.75</Subscript>Zn<Subscript>0.25</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> nickel zinc ferrite

We have developed processes for the synthesis of Ni_0.75Zn_0.25Fe_2–xLn_xO₄ ferrite solid solutions with the spinel structure and investigated the effect of the rare-earth elements Nd, Gd, Yb, and Lu on the chemical composition, extent, lattice parameters, and magnetic properties of the solid solutions. The results demonstrate that rare-earth solubility in the parent spinel reaches ≈2.5 at %, which leads to changes in the magnetic characteristics of the material, in particular in its saturation magnetization M_s, T_C, and coercive force H_c.     

Effect of Sn content on the dielectric and piezoelectric properties of the ternary system (0.975-<Emphasis Type="Italic">y</Emphasis>)BaTiO<Subscript>3</Subscript>–0.025SrTiO<Subscript>3</Subscript>–<Emphasis Type="Italic">y</Emphasis>BaSnO<Subscript>3</Subscript>

Design of the polymorphic phase composition in the (0.975-y)BaTiO₃–0.025SrTiO₃–yBaSnO₃; BT-ST-yBSn ternary system was based on the ferroelectric phase diagram. The dense ceramic of BT-ST-yBSn, with y = 0.00, 0.02, 0.04, 0.06, 0.08 and 0.10 compositions, was fabricated successfully via the solid-state reaction method. The effect of Sn substitution on the ferroelectric phase transition and piezoelectric properties was explored in order to achieve high-performance piezoelectric properties. All of the ceramics exhibited pure perovskite structures. Orthorhombic to tetragonal phase transition was evidenced clearly as a function of Sn content. The orthorhombic to tetragonal phase transition shifted close to ambient temperature by increasing the Sn content. The coexistent tetragonal and orthorhombic phases were exhibited at the composition, y = 0.04, and showed outstanding dielectric and piezoelectric properties, maximum relative permittivity (ε _{r max}) of 11500 and piezoelectric coefficient (d ₃₃) of 450 pC/N. An outstanding reversible strain of about 0.12%, with a normalized piezoelectric coefficient (S _max /E _max) of 1280 pm/V at a low electric field (10 kV/cm), was observed clearly at the composition of the coexistent phase. The BT-ST-BSn ceramics are the most promising candidate for lead-free piezoelectric materials.     

Phase equilibria and crystal structures of solid solutions in the system LaCoO<Subscript>3−δ</Subscript>-SrCoO<Subscript>2.5±δ</Subscript>-SrFeO<Subscript>3−δ</Subscript>-LaFeO<Subscript>3−δ</Subscript>

The composition region and structure of La_1?x Sr _x Co_1?y Fe _y O_3?δ solid solutions are determined by x-ray powder diffraction using the Rietveld profile analysis method. The solid solutions based on lanthanum cobaltite, LaCoO_3?δ, have a rhombohedrally distorted perovskite-like structure (sp. gr. R \(\bar 3\) c), and those based on lanthanum ferrite, LaFeO_3?δ, have an orthorhombically distorted structure (sp. gr. Pbnm). The rhombohedral distortion decreases with increasing strontium content, and the solid solutions with x ≥ 0.5 have an ideal cubic structure (sp. gr. Pm3m). The composition dependences of lattice parameters for the La_1?x Sr _x Co_1?y Fe _y O_3?δ solid solutions are presented, and the 1100°C isotherm of the LaCoO_3?δ-SrCoO_2.5±δ-SrFeO_3?δ-LaFeO_3?δ system in air is constructed.     

Phase equilibria and crystal structures of solid solutions in the Sr-Fe-Ni-O system at 1100°C in air

The phase equilibria in the Sr-Fe-Ni-O system at 1100°C in air have been studied by x-ray diffraction, and the corresponding phase diagram at constant temperature and pressure has been constructed. The system has been shown to contain two solid-solution series at 1100°C in air: SrFe_{1 ? x} Ni _x O_{3 ? δ} (0 < x ≤ 0.075, sp. gr. Cmmm) and Sr₃(Fe_{1 ? y} Ni _y )₂O_{7 ? δ} (0 < y ≤ 0.15, sp. gr. I4/mmm). Neither Sr₄(Fe_{1 ? z} Ni _z )₆O₁₃ nor Sr(Fe_{1 ? z} Ni _z )₁₂O₁₉ solid solutions have been identified. The lattice constants and structural parameters of single-phase samples have been refined by the full profile Rietveld analysis method.     

Irreversibility Line Measurement and Vortex Dynamics in High Magnetic Fields in Ni- and Co-Doped Iron Pnictide Bulk Superconductors

The de-pinning or irreversibility lines were determined by ac susceptibility, magnetization, radio-frequency proximity detector oscillator (PDO), and resistivity methods in Ba(Fe_0.92Co_0.08)₂As₂ ( T _c = 23.2 K), Ba(Fe_0.95Ni_0.05)₂As₂ ( T _c = 20.4 K), and Ba(Fe_0.94Ni_0.06)₂As₂ ( T _c = 18.5 K) bulk superconductors in ac, dc, and pulsed magnetic fields up to 65 T. A new method of extracting the irreversibility fields from the radio-frequency proximity detector oscillator induction technique is described. Wide temperature broadening of the irreversibility lines, for any given combination of ac and dc fields, is dependent on the time frame of measurement. Increasing the magnetic field sweep rate (dH/dt) shifts the irreversibility lines to higher temperatures up to about dH/d t = 40,000 Oe/s; for higher dH/dt, there is little impact on the irreversibility line. There is an excellent data match between the irreversibility fields obtained from magnetization hysteresis loops, PDO, and ac susceptibility measurements, but not from resistivity measurements in these materials. Lower critical field vs. temperature phase diagrams are measured. Their very low values near 0 T indicate that these materials are in mixed state in nonzero magnetic fields, and yet the strength of the vortex pinning enables very high irreversibility fields, as high as 51 T at 1.5 K for the Ba(Fe_0.92Co_0.08)₂As₂ polycrystalline sample, showing a promise for liquid helium temperature applications.     

Low-temperature acoustic properties of single-crystal hafnium

Five independent adiabatic elastic tensor components c _ij of single-crystal Hf (0.3% Zr) have been precisely measured in the range 78–300 (c ₁₁ and c ₃₃) or 78–160 K (c ₁₂, c ₁₃, and c ₄₄) at 50 MHz using an ultrasonic pulse technique. The corresponding linear absorption coefficients α _ij (T) have been measured in the same temperature ranges. The c _ij data have been used to determine adiabatic compressibilities β_∥ and β_⊥, and Young’s moduli E _∥ and E _⊥ along and across the c axis, respectively. Near 140 K, we have revealed an anomaly in c ₃₃(T) due to changes in the phonon spectrum of single-crystal α-Hf. The observed anomalies in temperature-dependent α₁₁ and α₃₃ are tentatively attributed to grown-in dislocations.