We present polarization- and temperature-dependent Raman spectroscopic study of hexagonal tungsten bronze, K_(0.3)WO_3. The observed asymmetry in phonon line shapes indicate the presence of strong lattice anharmonicity arising due to the nonstoichiometry of the material. We observed a broad multipeak Raman feature at low frequency due to the local modes of K atoms known as local structural excitations. The observed vibrational features indicate a second-order phase transition around T=200 K accompanied by a frequency softening of low-frequency phonon modes. The observed phonon anomalies hint a physical picture involving a continuous symmetry change toward a charge-ordered state below 200 K. These observations indicate that K_(0.3)WO_3 may exhibit a weak charge-density-wave ground state at low temperatures
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