Barium and strontium carbonate with various nonequilibrium morphologies were grown in the presence of poly(acrylic acid) sodium salt to induce the polymer-induced liquid-precursor (PILP) process. Previously, the PILP process had only been demonstrated for calcium carbonate but with indirect evidence suggesting it can be induced in calcium phosphate and barium carbonate. In this report, further evidence to suggest a similar liquid-phase amorphous precursor can be generated for both barium and strontium carbonate is presented, and these phases were used to synthesize various unique morphologies in the transformed crystals, including films, fibers, and cones. On the basis of the nanogranular texture of the fibers, a new mechanism for fiber formation is proposed, which combines a permutation of our former solution−precursor−solid (SPS) mechanism with mesocrystal assembly. This hypothesis includes an autocatalytic assembly of nanodroplets/nanoparticles at high energy surface protrusions as a means for generating the one-dimensional growth of fibers. These findings support the premise that the PILP process is nonspecific and applicable to many different ionic salt crystal systems.

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We study and compare high coupling symmetric and shear mode Lamb wave resonators realized in thin plates of X-cut lithium niobate. Fundamental mode bar resonators with a plate width of 20 µm, a plate thickness of 1.5 µm, apertures of 50, 90 and 130 µm and acoustic wave propagation rotated 30 • (symmetric) and 170 • (shear) to the +y-axis were realized on a single die for direct comparison. As expected, the symmetric Lamb wave resonators exhibited a higher sound velocity of ~6400 m/s when compared to the shear velocity of ~3900 m/s. The shear mode resonators, however, were found to have a significantly higher effective piezoelectric coupling coefficient of 16.3%, compared to a maximum of 9.1% for the symmetric Lamb wave resonators. In addition, the shear mode resonators were found to be less sensitive to the device aperture and to have fewer spurious responses. Based on these results, the shear mode resonators were selected for scaling to higher operating frequencies. A shear mode lithium niobate Lamb wave resonator operating at 350 MHz has been demonstrated with an effective piezoelectric coupling of 16%, a quality factor in air of 2200 and a device figure-of-merit of 420, among the highest reported for Lamb wave resonators [1-3].