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A model to predict material characteristics of the InGaN ternary system, which is useful for blue and green light emitting and laser diodes, with respect to an unstable two-phase region in the phase field and the first neighbor anion–cation bond length is developed. The unstable region is analyzed using a strictly regular solution model. The interaction parameter used in the analysis is obtained from a strain energy calculation using the valence force field (VFF) model, modified for both wurtzite and zinc-blende structures to avoid overestimation of the strain energy. The structural deviation from an ideal wurtzite structure in GaN and InN is also taken into account in our model. The critical temperatures found in our analysis for wurtzite InGaN and zinc-blende InGaN are 1967 and 1668 K, respectively. This suggests that, at typical growth temperatures around 800 °C, a wide unstable two-phase region exists in both wurtzite and zinc-blende structures. The modified VFF model can also predict the microscopic crystal structure, such as first neighbor anion–cation bond lengths. In order to validate our calculation results for zinc-blende structures, we compare the calculated and the experimental results in terms of the interaction parameter and the first neighbor anion–cation bond lengths in the InGaAs system. For the wurtzite structure, we compare the calculated and the experimental results for the first neighbor anion–cation bond lengths in the InGaN system. The calculated results agree well with the experimental results.

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The Group III-nitride ternary system is studied with respect to an unstable two-phase region in the phase field. The unstable two-phase region is analyzed using a strictly regular solution model. The interaction parameter used in the analysis is obtained from a strain energy calculation using the valence force field model, modified for both wurtzite and zinc-blende structures to avoid overestimation of the strain energy. The structural deviation from an ideal wurtzite structure in InN, GaN, and AlN is also taken into account in our model. According to the calculated results of the interaction parameters, the critical temperature for wurtzite InGaN, InAlN, and GaAlN are found to be 1967 K, 3399 K, and 181 K, respectively. This suggests that, at a typical growth temperature of 800–1000°C a wide unstable two-phase region exists in both InGaN and InAlN. In order to show the validity of our calculation results, we compare the calculated results and the experimental results using the calculation of the interaction parameter for the InGaAs system. The calculated results agree well with the experimental results.

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-Purpose. This study aimed to develop a novel approach for predicting the oral absorption of low-solubility drugs by considering regional differences in solubility and permeability within the gastrointestinal (GI) tract. Methods. Simulated GI fluids were prepared to reflect rat in vivo bile acid and phospholipid concentrations in the upper and lower small intestine. The saturated solubility and permeability of griseofulvin (GF) and albendazole (AZ), a drug with low aqueous solubility, were measured using these simulated fluids, and fraction absorbed (Fa) at time t after oral administration was calculated. Results. The saturated solubility of GF and AZ, a drug with low aqueous solubility, differed considerably between the simulated GI fluids. Large regional differences in drugs concentration were also observed following oral administration in vivo. The predicted Fa values using solubility and permeability data of the simulated GI fluid were found to correspond closely to the in vivo data. Conclusion. These results indicated the importance of evaluating regional differences in drug solubility and permeability in order to predict oral absorption of low-solubility drugs accurately. The new methodology developed in the present study could be useful for new oral drug development.

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