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RESEARCH/RESEARCHERS ness of the TeSW-prepared p-Si is very thin ing orientation. Some recent studies have such efforts for PZN-PT. In the August and the rms roughness is only 1.6 nm. reported frictional differences, or aniso- issue of the Journal of the American Ceramic The researchers also performed a con- tropy, less than a factor of 3 for incom- Society (p. 2310; DOI: 10.111/j.1551- trolled experiment of p-Si formation using mensurate crystal surfaces when there 2916.2005.00391.x), G. Deng and col- NaOH etchant at various pH levels, but were periodicity differences. leagues from the Shanghai Institute of they observed no efficient PL emission To measure the frictional effects due to Ceramics, China, have reported their suc- from any of the NaOH-prepared samples. periodicity alone and not to other factors cess in synthesizing pure perovskite The researchers pointed out that the such as chemical differences, the re- ceramics of PZN-PZT, as an alternative to reproducibility appeared to be a problem searchers worked with decagonal quasi- PZN-PT, near their MPB. The researchers for the photoetched p-Si synthesis tech- crystals of an aluminum-nickel-cobalt (Al- have observed much higher piezoelectric nique. They point out that others have Ni-Co) alloy. Stacked planes of Al-Ni-Co and electromechanical coupling coeffi- suggested that the preexisting state of the crystals exhibit both tenfold and twofold cients for their newly synthesized mate- Si surface plays a decisive role in deter- rotational symmetry. By cutting a single rial than those reported earlier. mining p-Si formation. Al-Ni-Co quasicrystal parallel to its ten- Because their goal was to find good TAO XU fold axis, the researchers were able to pro- piezoelectric values, the researchers ex- duce a two-dimensional surface with one plored 0.3Pb(Zn1/3Nb2/3)O3-0.7Pb0.96La0.04 High Frictional Anisotropy Found periodic axis and one aperiodic axis, sepa- (ZrxTi1–x)0.99O3 [La-doped 0.3PZN- on Quasicrystal Surface rated by 90°. In order to avoid surface 0.7PZT], with x ranging from 50 to 53 A collaboration of scientists from damage and also wear of the tip used in stepwise by 0.5 (i.e., values around the Lawrence Berkeley National Laboratory the combined AFM–STM instrument, a MPB). The samples were prepared by the (Berkeley Lab) and the Ames Laboratory at TiN tip passivated with a molecular layer two-step hot-pressing process. X-ray dif- Iowa State University have determined that of hexadecane thiol was used. fractometry (XRD) revealed that the friction along the surface of a quasicrystal “Strong friction anisotropy was microstructures of these complex com- in the direction of a periodic geometric con- observed when the AFM tip slid along the pounds experience a gradual transition figuration is about eight times greater than two directions: high friction along the peri- process from tetragonal to rhombohedral in the direction where the geometric con- odic direction, and low friction along the phase with an increase in the Zr/Ti ratio. figuration is aperiodic (i.e., without regu- aperiodic direction,” said co-researcher The MPB is defined as the coexistence of larity). In an article published in the August J.Y. Park of Berkeley Lab. “We believe the tetragonal and rhombohedral phases. 26 issue of Science (p. 1354), the research source of this friction has both an elec- Therefore, the research team deduced collaboration led by Miquel Salmeron, a tronic and a phononic contribution.” that the MPB in their samples can be physicist with Berkeley Lab’s Materials Phonons are quantized vibrations in a delimited in the range of Zr/Ti = Sciences Division, and Patricia Thiel, a crystal lattice. The frictional anisotropy 51/49–52/48. In addition, XRD revealed chemist in Ames Lab, reports that geomet- vanished when the samples were oxi- that samples in the entire composition ric periodicity was confirmed by rows of dized by exposure to air. range had pure perovskite structure. The atoms that formed a Fibonacci sequence, a The researchers said that new theoreti- piezoelectric coefficient (d33) was mea- numerical pattern often observed in quasi- cal models are needed to determine sured using a quasi-static piezoelectric d33 crystals. The research combined the use of whether the electronic or phononic con- meter. The maximum of d33 was found to scanning tunneling microscopy (STM) and tributions dominate the observed fric- be 845 pC/N for Zr/Ti = 51/49, which atomic force microscopy (AFM) to observe tional anisotropy. the researchers indicate is much higher the surface structures and measure the fric- than the previously reported value of 670 tional forces. La-Doped 0.3PZN-0.7PZT pC/N. Electromechanical coupling was “That we can get such a large differ- Ceramics with Pure Perovskite measured using an impedance analyzer, ence in frictional force just by scratching Phase Synthesized and its maximum value was observed to the surface of a material in a different It is well known that the single-crystal be 0.7 for the same composition Zr/Ti = direction was a major surprise,” said relaxor ferroelectrics, Pb(Zn1/3Nb2/3)O3- 51/49 and larger than the previously Salmeron. “Our results reveal a strong PbTiO3 (PZN-PT) and Pb(Mg1/3Nb2/3)O3- reported value of 0.65. Dielectric coefficient connection between interface atomic PbTiO3 (PMN-PT), possess ultrahigh and dielectric loss were measured using structure and the mechanisms by which piezoelectric properties. However, in the impedance analyzer. This series of frictional energy is dissipated.” comparison with single crystals, ceramics piezoelectric ceramics have high Tmax At the atomic level, when two surfaces have advantages including low produc- (206–213°C) and large dielectric constants come in contact, the chemical bonds and tion cost, homogeneous compositions, (3321–4088 for poled and 2048–2796 for clouds of electrons in their respective tunable properties for applications such depoled samples). The researchers con- atoms create frictional force and cause as medical ultrasonic probes and micro- cluded that these high values of piezoelec- energy to be dissipated. It has long been fine actuators. Although pure perovskite tric properties make 0.3PZN-0.7PLZT an known that friction is greater between PMN-PT ceramics have been synthesized interesting material for potential applica- surfaces of identical crystallographic ori- near their morphotropic phase boundary tions in transducers, actuators, and probes. entation than between surfaces of differ- (MPB), until now success has eluded VIVEK RANJAN MRS Materials Connections Your source for Materials Research-Related Information! Research news, materials data sources, www.mrs.org/connections/ materials Web site database, meetings calendar, and more. Check it out today! 690 MRS BULLETIN • VOLUME 30 • OCTOBER 2005 RESEARCH/RESEARCHERS News of MRS Members/Materials Researchers In Memoriam and rapid solidification of alloys. His work Survey of Materials Science and Engi- Morris Cohen, Insti- resulted in a much more basic understand- neering). This highly influential report tute Professor Emeritus ing of how to make steel strong and made became known as the “Cohen Report,” at the Massachusetts practical the ultrahigh-strength steels used reflecting Morris’s role in making this Institute of Technology, today. huge effort come to fruition. “Materials passed away May 27, Morris’s extensive service to the United and Man’s Needs” turned out to have a 2005, at his home in States included work on committees of the very large influence on national policy Swampscott, Mass. He National Academy of Sciences, the and on materials education and research. was 93. National Science Foundation, NASA, and Indeed, MIT was one of the first depart- Morris grew up in the National Academy of Engineering. ments to create a materials catholic pro- Chelsea, Mass., and en- During World War II, Morris served as gram under department head Walter rolled as a freshman at MIT in the fall of associate director of the Manhattan Project Owen, as the metallurgy department at 1929. By 1936, he had earned a ScD degree at MIT and also contributed to the pro- MIT transformed itself from a narrowly in Materials Science and Engineering and grams at Los Alamos National Labora- focused metals-based effort to become was appointed an instructor in metallurgy. tory, the Oak Ridge facilities in Tennessee, the broadly defined MSE program that is He became a full professor in 1946, was and the Hanford Site in Washington. He vibrantly continuing today. named Ford Professor of Metallurgy in published nearly 300 refereed research Cohen was preceded in death by his 1962, and was recognized across MIT by papers and had more than 150 graduate wife, Ruth, and his daughter, Barbara promotion to Institute Professor in 1975. and postdoctoral students. In 1977, Morris Norwind. He is survived by his son Joel; Morris Cohen’s contributions to the was awarded the National Medal of two sisters, Louise Polansky and Charlotte field of science, especially materials sci- Science, and in 1987, he received the Freed; three grandchildren and five great- ence, were broad and deep—from funda- Kyoto Prize in Advanced Technology. grandchildren. Morris’s scientific vision, mental investigations on the properties of Morris was a visionary in helping to dedication, and talent, along with his iron and steel, especially the martensitic create the new field of materials science warm personality and friendship, will be transformation in steel and how micro- and engineering. In the early 1970s, the deeply missed by all who knew him. An structure improves the mechanical proper- National Academy undertook a study of endowed MSE Graduate Fellowship at ties of steel, to seminal contributions to the the field of materials science and engi- MIT is currently being raised in his honor. mechanism and kinetics of the martensitic neering.