Optical conductivity measurements on the perovskite-related oxide CaCu3Ti4O12 provide a hint of the physics underlying the observed giant dielectric effect in this material. A low-frequency vibration displays anomalous behavior, implying that there is a redistribution of charge within the unit cell at low temperature. At infrared frequencies (terahertz), the value for the dielectric constant is approximately 80 at room temperature, which is far smaller than the value of approximately 10(5) obtained at lower radio frequencies (kilohertz). This discrepancy implies the presence of a strong absorption at very low frequencies due to dipole relaxation. At room temperature, the characteristic relaxation times are fast (less than or approximately 500 nanoseconds) but increase dramatically at low temperature, suggesting that the large change in dielectric constant may be due to a relaxor-like dynamical slowing down of dipolar fluctuations in nanosize domains.

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Neutron scattering is an extremely powerful tool in the study of elemental excitations in condensed matter. This book provides a practical guide to basic techniques using a triple-axis spectrometer. Introductory chapters summarize useful scattering formulas and describe the components of a spectrometer, followed by a comprehensive discussion of the resolution function and focusing effects. Later sections include simple examples of phonon and magnon measurements, and an analysis of spurious effects in both inelastic and elastic measurements, and how to avoid them. Finally, polarization analysis techniques and their applications are covered. This guide will allow graduate students and experienced researchers new to neutron scattering to make the most efficient use of their experimental time.

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The cubic perovskite-related ceramic CaCu 3 Ti 4 O 12 has a very high static dielectric constant 0 տ10 000 at room temperature ͑RT͒, which drops to about 100 below Ӎ100 K. Substituting Cd for Ca reduces the RT value of 0 by over an order of magnitude. The origin of the large 0 is not fully understood, but may be due to an internal barrier layer capacitance ͑IBLC͒ effect. Infrared measurements on the Ca and Cd compounds show that low-frequency modes increase dramatically in strength at low temperature, suggesting a change in the effective charges and increasing electronic localization that may lead to a breakdown of the IBLC effect.High dielectric constant materials find numerous technological applications. In the case of memory devices based on capacitive components, such as static and dynamic random access memories, the static dielectric constant 0 will ultimately decide the level of miniaturization. The dielectric constant of a material is related to the polarizability ␣, in particular, the dipole polarizability ͑an atomic property͒, which arises from structures with a permanent electric dipole which can change orientation in an applied electric field. These two quantities are linked through the ClausiusMossotti relation. In insulators 0 Ͼ0; materials with a dielectric constant greater than that of silicon nitride ( 0 Ͼ7) are classified as ''high dielectric constant'' materials. In general, a value of 0 above 1000 is related to either a ferroelectric which exhibits a dipole moment in the absence of an external electric field, or a relaxor characterized by a ferroelectric response under high electric fields at low temperature, but no macroscopic spontaneous polarization. However, both classes of materials show a peak in 0 as a function of temperature, which is undesirable for many applications. The body-centered cubic perovskite-related material CaCu 3 Ti 4 O 12 shown in Fig.

We report results of elastic and inelastic neutron scattering experiments in the trivalent spinfluctuation metal CeIn3, Antiferrornagnetic order occurs at 10.23 + 0.01 K. The magnetic reflections can be indexed on a doubled chemical cell of cubic symmetry. The saturated ordered moment 0.65+ 0. 1@8 per cerium atom is comparable to the value 0.71p& expected for ordering within the 17 doublet, which is the ground level expected for J = 2 cerium moments in a cubic crystal field. The critical behavior of the order parameter is of the form Mst (T)/Mst (0) =A [(T& -T)/T&] & where M" is the staggered magnetization, A =2.2+0.2 and P=0.42 +0.02; in addition the critical fluctuations are extremely weak. We discuss this nearly meanfield behavior in the context of recent theories which describe critical behavior in systems where the critical temperature is much smaller than a characteristic spin-fluctuation temperature. The inelastic scattering measurements provide evidence for the existence of such a characteristic energy. At low temperatures the inelastic cross section is dominated by an anomalously broad magnetic scattering peak, centered near 13 meV and with a half-width of about 10 meV. We interpret the large linewidth as arising from fast spin fluctuations, which arise from strong Kondo-type exchange coupling of the 4 f spins to the conduction electrons.