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Transition between the low- and high-density amorphous H2O was observed with a piston-cylinder apparatus from 77 K to 140 K, almost the glass-transition temperature of the amorphs. The transition was found to occur reversibly and abruptly at ∼135 K and ∼0.2 GPa with a volume change of 0.20±∼0.01 cm3/g and some hysteresis. This confirmed the transition to be first order. Absence of intermediate amorphous states between the low-density and high-density amorphs suggested existence of two substantially different liquid phases near the glass-transition temperature.

Nature © Macmillan Publishers Ltd 1998 8 letters to nature 164 NATURE | VOL 392 | 12 MARCH 1998the target range for DRAM applications (1-5 ϫ 10 Ϫ 7 A cm Ϫ 2 ). At this composition, we find e r ¼ 62:5 and the FOM is 24.3 C cm −2 .These results should be contrasted with those of bulk crystalline Zr x Sn y Ti z O 4 (x þ y þ z ¼ 2) (ref. 12). A single homogeneous solidsolution phase, isomorphous with the orthorhombic a-PbO 2 structure, was found near the composition ZrTiO 4 , as indicated in Fig. 2. The remainder of the Zr x Sn y Ti z O 4 phase diagram consists of multiphase mixtures of the ternary phase and the endmembers. Zr-Sn-Ti-O polycrystalline ceramics are well known for their superior microwave properties, including a moderate dielectric constant, very low dissipation factor, and low temperature coefficient of permittivity 13 . The properties of Zr 0.875 Sn 0.25 Ti 0.875 O 2 , for example, were studied carefully as a function of doping and sintering. A permittivity of ϳ36 and values for the dissipation factor (tan dϳ1=Q) as low as 7 ϫ 10 Ϫ 5 were obtained. The indicated composition is typical of those used for applications, which are invariably chosen to be within the homogeneous phase field. Note that the optimum compositions in our amorphous films are outside this composition field that yields homogeneous crystalline phases.Amorphous thin films of (Zr, Sn)TiO 4 with a particular but unspecified Zr:Sn composition have been studied 14 : a value of e r ¼ 27 was inferred in amorphous films prepared by radio frequency magnetron sputtering at 200 ЊC; a value of e r ¼ 38 was found in crystalline films, that is, the bulk value. For approximately the same composition, however, we observe eϳ50. This is a very substantial difference. At present we cannot explain the discrepancy between our data and those described in ref. 14. We do observe a decrease in the dielectric constant for deposition at higher temperatures, namely for films with a presumably greater degree of local order, so perhaps the films deposited by Nakagawara et al. 14 also have a higher degree of order than our films.This work demonstrates the value of the CCS technique in the search for metastable materials whose properties are sensitive to preparation conditions. Many issues regarding the development of this material for practical application remain to be addressed. For example, fully optimized uniform films need to be made using a single target with on-axis sputtering (or using CVD), and the properties of films ϳ10-20 nm thick (one fifth the present value) must be evaluated. Also, conditions that lead to a lower leakage current must be found and capacitors made using standard electrodes (for example, TiN) must be subjected to standard postprocessing and evaluated for reliability using accelerated testing. Although Zr-Sn-Ti-O films must be further developed, our preliminary results are encouraging. Ⅺ

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The volume of water (H(2)O) was obtained at about 200-275 K and 40-400 MPa by using emulsified water. The plot of volume against temperature showed slightly concave-downward curvature at pressures higher than ≈200 MPa. This is compatible with the liquid-liquid critical-point hypothesis, but hardly with the singularity-free scenario. When the critical point is assumed to exist at ≈50 MPa and ≈223 K, the experimental volume and the derived compressibility are qualitatively described by the modified Fuentevilla-Anisimov scaling equation.

According to the liquid-liquid critical-point hypothesis about water, two liquid waters exist at low temperatures and are supposed to be merged at a critical point. The low-temperature metastable melting curves of D2O ices have been measured. It is found that the melting curve of D2O ice III is smoothly curved around 25 MPa and 238 K, whereas the melting curve of D2O ice IV undergoes an abrupt change of slope at 100 MPa and 220 K. This is consistent with the existence of a liquid-liquid critical point in the region between the melting curve of D2O ice III and the melting curve of D2O ice IV.