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One of the qualities that distinguishes living systems from inanimate matter is the ability to adapt to changes in the environment. Smart materials have the ability to perform both sensing and actuating functions and are, therefore, capable of imitating this rudimentary aspect of life. Four of the most widely used smart materials are piezoelectric Pb(Zr, Ti)O 3 , electrostrictive Pb(Mg, Nb)O 3 , magnetostrictive (Tb, Dy)Fe 2 and the shape-memory alloy NiTi. All four are ferroic with active domain walls and two phase transformations, which help to tune the properties of these actuator materials. Pb(Zr, Ti)O 3 is a ferroelectric ceramic which is cubic at high temperature and becomes ferroelectric on cooling through the Curie temperature. At room temperature, it is poised on a rhombohedral-tetragonal phase boundary which enhances the piezoelectric coefficients. Terfenol, (Tb, Dy)Fe 2 , is also cubic at high temperature and then becomes magnetic on cooling through its Curie temperature. At room temperature, it too is poised on a rhombohedral-tetragonal transition which enhances its magnetostriction coefficients. Pb(Mg, Nb)O 3 and nitinol (NiTi) are also cubic at high temperatures and on annealing transform to a partially ordered state. On further cooling, Pb(Mg, Nb)O 3 passes through a diffuse phase transformation at room temperature where it exhibits very large dielectric and electrostrictive coefficients. Just below room temperature, it transforms to a ferroelectric rhombohedral phase. The partially ordered shape-memory alloy NiTi undergoes an austenitic (cubic) to martensitic (monoclinic) phase change just above room temperature. It is easily deformed in the martensitic state but recovers its original shape when reheated to austenite. The structural similarities between these four superb actuator materials are remarkable, and provide a key to the development of future smart materials.

Contents: Distribution Functions of Coexisting Phases in a Complete Solid Solution System; The Glassy Behaviour of Relaxor Ferroelectrics; The Dielectric Relaxation of Lead Magnesium Niobate Relaxor Ferroelectrics; Anelastic Relaxation and Internal Strain in Lead Magnesium Niobate Relaxors; Dipolar-Glass Model for Lead Magnesium Niobate, Ferroelectric Properties of Lead Barium Niobate Compositions Near the Morphotropic Phase Boundary, Pyroelectric Properties of Lead Barium Niobate Single Crystals, Microstructure-Property Relations in Tungsten Bronze Lead Barium Niobate, Pb(1-x)BaxNb2O6, An Investigation of the Lead Scandium Tantalate-Lead Titanate Solid Solution System, Pyroelectric Response and Depolarization Behaviour of (1-x)Pb(Sc(1/2) Ta(1/2)O3 - (x)PbTiO3 Materials, Pyroelectric and Dielectric Properties of PMN- Based Ceramics Under DC Bias, Chemical Reactions of Lead Magnesium Niobate Titanate in the Presence of a Glass, La2Ti2O7 Ceramics, Effects of pH and H2O2 Upon Coprecipitated PbTiO3 Powders, and Kinetics of the Hydrothermal Crystallization of the Perovskite Lead Titanate.

Using a neodymium glass laser and time-synchronized pulse detection, second harmonic signals were observed from a number of clay mineral powders. The second harmonic generation (SHG) experiments provide the first physical evidence (other than diffraction patterns) for the polar nature of the kaolinite layer and its stacking sequences. Well-crystallized nacrite and dickite specimens gave signals comparable to those of quartz, but the SHG intensities from the smaller kaolinite and halloysite crystallites were noticeably weaker. Based on results from eight specimens, there appears to be a direct correlation between SHG intensity and particle size, similar to that reported previously for quartz.

The theory of secondary ferroics is applied to quartz. Our studies of quartz are summarized, and the recent work on twin wall orientations and switching dynamics is detailed.

Calcium doped barium titanate ceramics with composition (Ba0.95Ca0. 05) (Ti1−yCay)O3−y prepared by a liquid mixing technique were used to measure the dielectric properties. The pure barium titanate and lightly-Ca-doped materials obey a Curie Weiss law when the temperature is above the Curie temperature. It has been found that the average cubic-tetragonal phase transition temperature moves downward when the octahedrally-coordinated Ca concentration increases, and heavily-Ca-doped barium titanate ceramics show relaxor behavior with a diffuse phase transition characteristic (DPT). Above the average transition temperature Tav the dielectric properties for heavily doped materials do not obey the Curie Weiss law, but can be described by a quadratic relation over a wide range of temperature. Experiments have shown that there exists an extra K(T) peak attributable to the existence of separate microregions of Ba0.95Ca0.05TiO3 in a matrix of (Ba0.95Ca0.05) (Ti1−yCay)O3−y (where y ≤ 2%).

A new type of piezoelectric PZT-polymer 1-3-0 composite was fabricated with a single large void present in the center of the composite. Experimentally and theoretically the addition of this type of void to a 1–3 composite significantly enhances the hydrostatic piezoelectric [dbar] h and [gbar] h coefficients. A comparison of the experimental results and theoretical predictions was made. The pressure and frequency dependences of the properties of the 1-3 and 1-3-0 composites were measured, along with the effect of hydrostatic pressure cycling. The 1-3-0 composites partially depoled from pressure cycling to 600 psi (4.1 MPa), indicating that the limit of hydrostatic sensitivity, physically possible for the soft PZT used, was exceeded.

Various devices are described which record physical phenomena and which respond by transmitting signals via information processing units to actuators. For example, a thermistor senses temperature and transmits an electrical signal to an integrated circuit which may in turn actuate a furnace control. This review emphasizes the structure-property relationships of the sensor materials. An ionic conductor, such as stabilized zirconia, can be used to detect oxygen in air/fuel mixtures; metal oxides of large surface area can monitor humidity by surface conduction; and semiconducting transition-metal oxides can measure pH. The mechanism of vanadium dioxide critical temperature thermistors is described; as well as the operation of thermistors of negative and positive temperature coefficients (NTC and PTC) made from, for example, doped nickel oxide and barium titanate respectively. Composite sensors of two or more phases have properties which are the product of those of the individual components and have ...

Composites of PZT and polymer with 3-1 and 3-2 connectivity patterns have been fabricated by drilling holes in sintered PZT blocks and filling the holes with epoxy. The influence of hole size and volume fraction PZT on the hydrostatic properties of the composite was evaluated. By decoupling the piezoelectric [dbar]33 and [dbar]31 coefficients in the composite, the hydrostatic coefficients are greatly enhanced. On samples optimized for hydrophone performance, the dielectric constants of 3-1 and 3-2 composites are 600 and 300 respectively. The piezoelectric coefficients [dbar]h, [gbar]h, and [dbar]hdh for 3-1 composites are 230 (pCN−1), 34 (x10−3 VmN−1), and 7800 (10−15 m2N−1) respectively, and the corresponding values for 3-2 composites are 372 (pCN−1), 123 (10−3 VmN−1), and 45000 (10−15 m2N−1).

SummaryThe Ceylonese gemstone sinhalite, AlMgBO4, is isomorphous with olivine and chrysoberyl. Aluminium and magnesium are oetahedrally coordinated and boron occupies slightly distorted tetrahedra. Because of size differences, the smaller Al ion can be assigned to the inversion symmetry sites, with Mg in mirror plane positions. Least-squares refinement based on single crystal X-ray data gave an accurate set of atomic coordinates with mean interatomic distances: Al-O 1·90, Mg-O 2·10, B-O 1·49 Å.

CaMnSiO4 crystallizes in the olivine structure and is antiferromagnetic below 9°K; magnetic-susceptibility measurements gave θ = 26°K and peff = 5.77 microB. The cation distribution and magnetic spin structure were established by neutron diffraction. Divalent manganese occupies the inversion centers with calcium in mirror plane positions, isostructural with CaMgSiO4. At low temperatures the Mn moments align in antiferromagnetic chains along b with spin directions collinear to c.

The magnetic structure of LiFePO4 has been determined from neutron diffraction data. Magnetic susceptibility measurements on polycrystalline material gave pelf= 5"45#m 0= 88 °K, and T~v = 50°K. Below the N6el temperature, the Fe 2÷ spins align in an antiferromagnetic array collinear with b. The magnetic space group is Pnma'. LiFePO4 is isostructural with olivine; the magnetic properties of the transition-metal olivines are summarized.

Cobalt orthosilicate, Co 2 SiO 4 , is isomorphous with the mineral olivine and is antiferromagnetic below 49°K. The Curie-Weiss law coefficients for the paramagnetic region are Peff = 5·09 μB and θ = 65 °K. A four-sublattice magnetic spin structure based on Co-O-Co superexchange interactions is proposed to explain the susceptibility data. Low-temperature neutron diffraction patterns substantiate the model and show that the spin direction is along b .

Single crystals of Pb3GeO5 were grown from the melt by the Czochralski technique. Based on observations of the domain structure under mechanical stress, and the presence of an SHG signal, the crystals are ferroelastic and possibly ferroelectric, but show no phase transitions up to the melting point (738°C). The powder pattern was indexed on a monoclinic unit cell: a= 5.235±0.006 b = 5.244± 0.007, c = 5.45± 0.01 A, β = 92°39′ + 6′, Z= 1. Intensity calculations suggest a close relation to the tetragonal Cd3SiO5 structure.

Using the pulse-superposition method, the second-order elastic stiffnesses of aquamarine were deter- mined to be C11 = 3.085, C33 = 2.834, C12 = 1.289, C13 = 1.185, C44 = 0.661 Mbar. Results for goshenite beryl are very similar. Initial pressure derivatives were also determined.

The susceptibility curve of Fe2TeO6 exhibits two peaks, a sharp one at 201°K and a broad one at 233°K. Mossbauer measurements have established the onset of long‐range order at 201°K. The broad peak is thought to be due to some form of short‐range ordering and two models which might be referred to as layering and pairing are considered as possible explanations. These results are also compared with the evidence of neutron‐diffraction experiments. The correlation of these various experiments shows that iron tellurate provides an example of a material with magnetically distinguishable short‐range and long‐range order. Some aspects of this ordering have been compared with “intramolecular antiferromagnetism,” otherwise known as “isolated clustering” in polymeric coordination compounds.