Solid State Phenomena Vol. 184

Abstract: We report internal friction and shear modulus measurements of several types of synthesized graphene films. They include reduced graphene oxide, chemical-vapor deposited (CVD) graphene films on thin nickel films and on copper foils. These films were transferred from their host substrate into a water bath, and re-deposited onto to a high-Q single crystal silicon mechanical double-paddle oscillator. A minimal thickness dependence of both internal friction and shear modulus was found for reduced graphene oxide films varying thickness from 4 to 90 nm and CVD graphene films on nickel from 6 to 8 nm. The shear modulus of these multilayered films averages 53 GPa. Their internal friction exhibits a temperature independent plateau below 10K. The values of the plateaus are similar for both the reduced graphene oxide films and CVD graphene films on nickel, and they are as high as the universal "glassy range" where the tunneling states dominated internal friction of amorphous solids lies. In contrast, CVD graphene films on copper foils are 90~95% single layer. The shear modulus of these single layer graphene films are about five times higher, averaging 280 GPa. Their low temperature internal friction is too small to measure within the uncertainty of our experiments. Our results demonstrate the dramatic difference in the elastic properties of multilayer and single layer graphene films.

Abstract: An audiofrequency (8.5 kHz) cantilever resonator with an extremely low background internal friction (Q^-1≈2×10^-8) at liquid helium temperatures has been developed. Above 30 K, the Q of the resonator is dominated by thermoelastic loss; Q^-1 is nearly exactly described by Zener’s formula for thermoelastic damping. Below 30 K, Q^-1 decreases monotonically with decreasing temperature, reaching a typical baseline of Q^-1=1.5×10^-8 at 400 mK.

Abstract: Anelastic and dielectric spectroscopy measurements are presented, which, together with previous measurements [1], clarify some controversial aspects of the phase diagram of PbZr_1xTi_xO₃ close to the border with the antiferroelectric (AFE) phase, and at the morphotropic phase boundary (MPB). No evidence is found of a border separating monoclinic (M) from rhombohedral (R) phases, supporting recent structural studies according to which the two phases coexist, with the fraction of M prevailing near the MPB. A large frequency independent softening at the MPB indicates a genuine M phase over only finely twinned R phase. A new phase transition is found in both the anelastic and dielectric spectra at x = 0.1, at a temperature T_IT between the Curie temperature T_C and the boundary T_T to the phases with tilted octahedra. Such a diffuse transition is interpreted as onset of disordered tilts, which finally become ordered below T_T. In this manner, the phase diagram of PZT is rationalised with respect to the common tendency of perovskites to undergo tilting when the mismatch between the cation sizes exceeds a threshold.

Abstract: Anelastic and dielectric relaxation measurements have been carried out on poled and unpoled samples of the ferroelectric perovskite (Na_0.5Bi_0.5)_1−xBa_xTiO₃ (NBT-xBT), with composition in the range between pure NBT and the morphotropic phase boundary, 0 ≤ x ≤ 0.08. The complex elastic compliance spectra contain clear indications of both the rhombohedral/tetragonal and tetragonal/cubic transitions, allowing the determination of the phase diagram, which is difficult to obtain by diffraction techniques due to the very low distortions in both the tetragonal and rhombohedral phases and to the structural disorder in the Na/Bi sublattice. An extensive study is made for concentrations in the region of the morphotropic boundary (x ∼ 0.06) in order to find possible signatures of monoclinic phase, as for the case of PbZr_1-xTi_xO₃ (PZT). The main features in the anelastic curves are compared with those in the dielectric spectra and are tentatively related to different modes of octahedral rotations and polar cation shifts.

Abstract: The paper presents recent results of ultrasonic investigation of Sn₂P₂S₆ family ferroelectric crystals and their solid solutions in the temperature range 100-300 K. It was shown that in Sn₂P₂(S,Se)₆ crystals the critical ultrasonic velocity slowing down for longitudinal waves propagating along main crystallographic directions is quite sharp and large. The relative change of longitudinal ultrasonic velocity along z-axis at the phase transition gradually increased from 10 % in pure Sn₂P₂S₆ till 25 % for sample with 0.4 content of Se. Such large velocity change causes the large ultrasonic attenuation anomaly. The increase of relaxation time: τ=τ₀/(T_C-T) leads to the increase of attenuation. Prefactor τ₀ was shown to be very small and the critical attenuation anomaly arises in the narrow temperature range close to phase transition. In the 0.4 Se sample the phase transition is of the first order because small thermal hysteresis exists. The ultrasonic velocity behaviour in the ferroelectric phase was described using Landau theory and free energy expansion including sixth order terms. For (Sn,Pb)₂P₂S₆ system the critical ultrasonic anomalies were smaller and the phase transition temperature substantially decreased (for 0.45 Pb sample the phase transition point was at T_c =140 K). The ultrasonic anomalies at phase transition in (Pb_xSn_1-x)₂P₂S₆ have large hysteresis showing that transition is of the first order, far from the critical point.

Abstract: The Young’s modulus and the elastic energy dissipation of polyethylene oxide (PEO)-based lithium battery electrolyte membranes have been studied in this work. The membranes, formed by pure PEO and doped by LiCF₃SO₃, Li₂S and ZrO₂, were studied within a 90 K - 400 K temperature range. We observed the glass transition around 230 K and the first-order phase transformation from the crystalline to the amorphous phase around 330 K on heating. We also measured the isothermal kinetics of the transition from the amorphous to the crystalline state and found that it is slower in doped PEO. Moreover, we showed that for both samples the transformation becomes slower as the temperature increases between 319 and 331 K. The experimental results suggest that the amorphous state is stable at 331 K for a few hours before the transformation takes place. Finally, the moisture effects on the mechanical properties of pure and doped PEO membranes are reported.

Abstract: The internal friction of the hyperstabilized martensite demonstrates very low values, both above and below the nominal martensitic transformation temperature, due to a pronounced pinning effect. Over a wide temperature range it is comparable with the level of damping in the parent phase. A study of the temperature dependence of the non-linear ultrasonic internal friction and its strain amplitude hysteresis indicates that the diffusion, assisted by dislocations/interfaces, is quite pronounced and in Ni-Fe-Ga and Cu-Al-Be alloys it operates at temperatures around 20 K. The renucleation of the lamellar parent phase during the reverse martensitic transformation close to 600 K is accompanied by an internal friction peak which demonstrates a substantial transitory contribution. After renucleation of the parent phase the samples recover a conventional martensitic transformation with the internal friction level in the martensite comparable to the one in non-stabilized samples. Observations of a relaxation peak in the parent phase of different alloys for temperatures just below the renucleation stage of the reverse transformation point to the essential role of diffusion in the nucleation of the parent phase in hyperstabilized martensites.

Abstract: Strain glass is a new type of glass state discovered recently in Ni-rich Ti-Ni ferroelastic alloys. It is formed by doping sufficient point defects such as solute atoms or alloying elements into a martensitic alloy to destroy the long range strain order generated by the diffusionless martensitic phase transformation. The strain glass was observed in an off-stoichiometric Heusler Au₇Cu₅Al₄ alloy by the mechanical spectrum analysis. The martensitic transformation was experimentally confirmed following the occurrence of strain glass transition during the cooling. It is different from the model developed mainly in Ni-Ti based alloys among which the martensitic transformation was totally suppressed once the strain glass transition takes place. We conclude that newly observed strain glass in an off-stoichiometric Au₇Cu₅Al₄ alloy belongs to one type of precursor phenomena.

Abstract: The effects of long-range atomic order and pinning of interfaces on anelastic properties of Cu-based martensite have been distinguished by means of studying strain amplitude dependences of internal friction and Young’s modulus defect, assuming that low-and high-amplitude stages of the strain amplitude dependence correspond to the oscillations within and beyond pinning atmospheres.

Abstract: The strain amplitude-independent and strain amplitude-dependent components of the internal friction in a Ni₄₅Mn_36.7In_13.3Co₅ metamagnetic shape memory alloy have been studied as function of temperature, strain amplitude and polarizing magnetic field. For ultrasonic oscillation frequency (91 kHz) and low strain amplitudes (10^-7-10^-5), the experimental results show that the internal friction in the ferromagnetic austenite is much higher than in non-magnetic martensite. We suggest that this unusual relationship is due to a high contribution of the magnetomechanical component to the internal friction of the ferromagnetic austenite.